Merge pull request #3095 from vitorpamplona/claude/amazing-ptolemy-26Nek

Use locale-aware date/time formatting throughout the app
2026-08-11 08:47:33 +00:00 · 2026-05-29 08:30:41 -04:00
parent 9a6400a6e3 aeadbbd276
commit fd88e2f8a5
23 changed files with 297 additions and 269 deletions
@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.ui.note
+
+import android.content.Context
+import android.text.format.DateFormat
+import java.text.SimpleDateFormat
+import java.util.Date
+import java.util.Locale
+
+/**
+ * Date/time formatters that respect the user's Android system settings:
+ *   - Date order (dd/mm/yyyy, mm/dd/yyyy, yyyy-mm-dd…) is derived from the
+ *     active [Locale] via [DateFormat.getBestDateTimePattern].
+ *   - 12-hour vs 24-hour clock follows the system setting via
+ *     [DateFormat.is24HourFormat] (which is the user's manual override on
+ *     top of the locale default).
+ *
+ * All formatters here use Unicode LDML skeletons. `j` and `jm` are intentionally
+ * avoided — `j` only picks 12/24 hour from the *locale*, not the user override.
+ * We pick the time skeleton explicitly based on [DateFormat.is24HourFormat].
+ */
+
+private fun timeSkeleton(context: Context): String = if (DateFormat.is24HourFormat(context)) "Hm" else "hma"
+
+private fun bestPattern(
+    context: Context,
+    skeletonBase: String,
+    includeTime: Boolean,
+): SimpleDateFormat {
+    val locale = Locale.getDefault()
+    val skeleton = if (includeTime) skeletonBase + timeSkeleton(context) else skeletonBase
+    return SimpleDateFormat(DateFormat.getBestDateTimePattern(locale, skeleton), locale)
+}
+
+/** Locale-aware month + day + short time (e.g. "May 28, 14:32" / "28 May, 2:32 PM"). */
+fun formatMonthDayTime(
+    epochSeconds: Long,
+    context: Context,
+): String = bestPattern(context, "MMMd", includeTime = true).format(Date(epochSeconds * 1000L))
+
+/** Locale-aware medium date (e.g. "May 28, 2026" / "28 May 2026" / "28.05.2026"). */
+fun formatMediumDate(
+    epochSeconds: Long,
+    context: Context,
+): String = DateFormat.getMediumDateFormat(context).format(Date(epochSeconds * 1000L))
+
+/** Locale-aware medium date + short time, respecting the system 12/24-hour setting. */
+fun formatMediumDateTime(
+    epochSeconds: Long,
+    context: Context,
+): String {
+    val date = DateFormat.getMediumDateFormat(context).format(Date(epochSeconds * 1000L))
+    val time = DateFormat.getTimeFormat(context).format(Date(epochSeconds * 1000L))
+    return "$date $time"
+}
@@ -50,9 +50,6 @@ import com.vitorpamplona.amethyst.ui.theme.Size5dp
 import com.vitorpamplona.amethyst.ui.theme.StdPadding
 import com.vitorpamplona.amethyst.ui.theme.placeholderText
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.displayUrl
-import java.time.Instant
-import java.time.ZoneId
-import java.time.format.DateTimeFormatter

@Composable
 fun RelayCompose(
@@ -145,9 +142,3 @@ fun RemoveRelayButton(onClick: () -> Unit) {
        Text(text = stringRes(R.string.remove))
    }
 }
-
-fun formattedDateTime(timestamp: Long): String =
-    Instant
-        .ofEpochSecond(timestamp)
-        .atZone(ZoneId.systemDefault())
-        .format(DateTimeFormatter.ofPattern("MMM d, uuuu hh:mm a"))
@@ -32,25 +32,47 @@ import java.util.Date
 import java.util.Locale
 import kotlin.math.round

-private const val YEAR_DATE_FORMAT = "MMM dd, yyyy"
-private const val MONTH_DATE_FORMAT = "MMM dd"
+// Skeletons follow Unicode LDML — DateFormat.getBestDateTimePattern picks the
+// correct locale-specific ordering (e.g. "MMM d, y" in en-US vs "d MMM y" in en-GB).
+private const val YEAR_SKELETON = "yMMMd"
+private const val MONTH_SKELETON = "MMMd"
+private const val YEAR_NO_DAY_SKELETON = "yMMM"

-private const val YEAR_NO_DAY_DATE_FORMAT = "MMM yyyy"
-private const val MONTH_NO_DAY_DATE_FORMAT = "MMM dd"
+/**
+ * Per-thread cached [SimpleDateFormat] keyed off the current default [Locale].
+ *
+ * `SimpleDateFormat` is mutable and not thread-safe, and these formatters are
+ * read from both the UI thread (composition) and background coroutines
+ * (e.g. `LocalCache.justVerify` logging failed event verifications). A bare
+ * `var` shared across threads would race on the formatter's internal Calendar.
+ * Using `ThreadLocal` gives each thread its own instance — no locks, no
+ * allocation per call, and we rebuild lazily on locale change.
+ */
+private class LocaleAwareFormatter(
+    private val skeleton: String,
+) {
+    private val cache = ThreadLocal<Pair<Locale, SimpleDateFormat>>()

-var locale: Locale = Locale.getDefault()
-var yearFormatter = SimpleDateFormat(YEAR_DATE_FORMAT, locale)
-var monthFormatter = SimpleDateFormat(MONTH_DATE_FORMAT, locale)
+    fun get(): SimpleDateFormat {
+        val current = Locale.getDefault()
+        val cached = cache.get()
+        if (cached != null && cached.first == current) return cached.second
+        val fresh = SimpleDateFormat(DateFormat.getBestDateTimePattern(current, skeleton), current)
+        cache.set(current to fresh)
+        return fresh
+    }
+}

-var yearNoDayFormatter = SimpleDateFormat(YEAR_NO_DAY_DATE_FORMAT, locale)
-var monthNoDayFormatter = SimpleDateFormat(MONTH_NO_DAY_DATE_FORMAT, locale)
+private val yearFormatter = LocaleAwareFormatter(YEAR_SKELETON)
+private val monthFormatter = LocaleAwareFormatter(MONTH_SKELETON)
+private val yearNoDayFormatter = LocaleAwareFormatter(YEAR_NO_DAY_SKELETON)

 /**
 * Formats a Unix timestamp (seconds) as an absolute date/time string, picking the
 * granularity from how far away the timestamp is:
- *   - same day → time only (e.g. "14:32" / "2:32 PM", locale-aware)
- *   - same year → "MMM dd, HH:mm"
- *   - older    → "MMM dd, yyyy"
+ *   - same day → time only (locale + system 12/24-hr aware via [DateFormat.getTimeFormat])
+ *   - same year → "Jan 5, 14:32" / "5 Jan 14:32" / "Jan 5, 2:32 PM" (locale + system aware)
+ *   - older    → "Jan 5, 2024" / "5 Jan 2024" (locale aware)
 *
 * Used by [com.vitorpamplona.amethyst.ui.note.elements.TimeAgo] when the user
 * taps the relative timestamp to reveal the absolute one.
@@ -63,12 +85,6 @@ fun timeAbsolute(
    if (time == null) return " "
    if (time == 0L) return prefix + stringRes(context, R.string.never)

-    if (locale != Locale.getDefault()) {
-        locale = Locale.getDefault()
-        yearFormatter = SimpleDateFormat(YEAR_DATE_FORMAT, locale)
-        monthFormatter = SimpleDateFormat(MONTH_DATE_FORMAT, locale)
-    }
-
    val timeMs = time * 1000
    val now = Calendar.getInstance()
    val then = Calendar.getInstance().apply { timeInMillis = timeMs }
@@ -80,8 +96,8 @@ fun timeAbsolute(

    return when {
        sameDay -> prefix + timeOfDay
-        sameYear -> prefix + monthFormatter.format(timeMs) + ", " + timeOfDay
-        else -> prefix + yearFormatter.format(timeMs)
+        sameYear -> prefix + monthFormatter.get().format(timeMs) + ", " + timeOfDay
+        else -> prefix + yearFormatter.get().format(timeMs)
    }
 }

@@ -106,26 +122,11 @@ fun timeAgo(

    return when {
        timeDifference > TimeUtils.ONE_YEAR -> {
-            // Dec 12, 2022
-
-            if (locale != Locale.getDefault()) {
-                locale = Locale.getDefault()
-                yearFormatter = SimpleDateFormat(YEAR_DATE_FORMAT, locale)
-                monthFormatter = SimpleDateFormat(MONTH_DATE_FORMAT, locale)
-            }
-
-            prefix + yearFormatter.format(time * 1000)
+            prefix + yearFormatter.get().format(time * 1000)
        }

        timeDifference > TimeUtils.ONE_MONTH -> {
-            // Dec 12
-            if (locale != Locale.getDefault()) {
-                locale = Locale.getDefault()
-                yearFormatter = SimpleDateFormat(YEAR_DATE_FORMAT, locale)
-                monthFormatter = SimpleDateFormat(MONTH_DATE_FORMAT, locale)
-            }
-
-            prefix + monthFormatter.format(time * 1000)
+            prefix + monthFormatter.get().format(time * 1000)
        }

        timeDifference > TimeUtils.ONE_DAY -> {
@@ -157,26 +158,11 @@ fun timeAgoNoDot(

    return when {
        timeDifference > TimeUtils.ONE_YEAR -> {
-            // Dec 12, 2022
-
-            if (locale != Locale.getDefault()) {
-                locale = Locale.getDefault()
-                yearFormatter = SimpleDateFormat(YEAR_DATE_FORMAT, locale)
-                monthFormatter = SimpleDateFormat(MONTH_DATE_FORMAT, locale)
-            }
-
-            yearFormatter.format(time * 1000)
+            yearFormatter.get().format(time * 1000)
        }

        timeDifference > TimeUtils.ONE_MONTH -> {
-            // Dec 12
-            if (locale != Locale.getDefault()) {
-                locale = Locale.getDefault()
-                yearFormatter = SimpleDateFormat(YEAR_DATE_FORMAT, locale)
-                monthFormatter = SimpleDateFormat(MONTH_DATE_FORMAT, locale)
-            }
-
-            monthFormatter.format(time * 1000)
+            monthFormatter.get().format(time * 1000)
        }

        timeDifference > TimeUtils.ONE_DAY -> {
@@ -208,26 +194,11 @@ fun timeAgoNoDotNoDay(

    return when {
        timeDifference > TimeUtils.ONE_YEAR -> {
-            // Dec 12, 2022
-
-            if (locale != Locale.getDefault()) {
-                locale = Locale.getDefault()
-                yearNoDayFormatter = SimpleDateFormat(YEAR_NO_DAY_DATE_FORMAT, locale)
-                monthNoDayFormatter = SimpleDateFormat(MONTH_NO_DAY_DATE_FORMAT, locale)
-            }
-
-            yearNoDayFormatter.format(time * 1000)
+            yearNoDayFormatter.get().format(time * 1000)
        }

        timeDifference > TimeUtils.ONE_MONTH -> {
-            // Dec 12
-            if (locale != Locale.getDefault()) {
-                locale = Locale.getDefault()
-                yearNoDayFormatter = SimpleDateFormat(YEAR_NO_DAY_DATE_FORMAT, locale)
-                monthNoDayFormatter = SimpleDateFormat(MONTH_NO_DAY_DATE_FORMAT, locale)
-            }
-
-            monthNoDayFormatter.format(time * 1000)
+            monthFormatter.get().format(time * 1000)
        }

        timeDifference > TimeUtils.ONE_DAY -> {
@@ -259,26 +230,11 @@ fun timeAheadNoDot(

    return when {
        timeDifference > TimeUtils.ONE_YEAR -> {
-            // Dec 12, 2022
-
-            if (locale != Locale.getDefault()) {
-                locale = Locale.getDefault()
-                yearFormatter = SimpleDateFormat(YEAR_DATE_FORMAT, locale)
-                monthFormatter = SimpleDateFormat(MONTH_DATE_FORMAT, locale)
-            }
-
-            yearFormatter.format(time * 1000)
+            yearFormatter.get().format(time * 1000)
        }

        timeDifference > TimeUtils.ONE_MONTH -> {
-            // Dec 12
-            if (locale != Locale.getDefault()) {
-                locale = Locale.getDefault()
-                yearFormatter = SimpleDateFormat(YEAR_DATE_FORMAT, locale)
-                monthFormatter = SimpleDateFormat(MONTH_DATE_FORMAT, locale)
-            }
-
-            monthFormatter.format(time * 1000)
+            monthFormatter.get().format(time * 1000)
        }

        timeDifference > TimeUtils.ONE_DAY -> {
@@ -310,24 +266,9 @@ fun dateFormatter(
    val timeDifference = TimeUtils.now() - time

    return if (timeDifference > TimeUtils.ONE_YEAR) {
-        // Dec 12, 2022
-
-        if (locale != Locale.getDefault()) {
-            locale = Locale.getDefault()
-            yearFormatter = SimpleDateFormat(YEAR_DATE_FORMAT, locale)
-            monthFormatter = SimpleDateFormat(MONTH_DATE_FORMAT, locale)
-        }
-
-        yearFormatter.format(time * 1000)
+        yearFormatter.get().format(time * 1000)
    } else if (timeDifference > TimeUtils.ONE_DAY) {
-        // Dec 12
-        if (locale != Locale.getDefault()) {
-            locale = Locale.getDefault()
-            yearFormatter = SimpleDateFormat(YEAR_DATE_FORMAT, locale)
-            monthFormatter = SimpleDateFormat(MONTH_DATE_FORMAT, locale)
-        }
-
-        monthFormatter.format(time * 1000)
+        monthFormatter.get().format(time * 1000)
    } else {
        today
    }
@@ -409,12 +350,7 @@ fun lastSeenSentence(
            }
        }

-    if (locale != Locale.getDefault()) {
-        locale = Locale.getDefault()
-        yearFormatter = SimpleDateFormat(YEAR_DATE_FORMAT, locale)
-        monthFormatter = SimpleDateFormat(MONTH_DATE_FORMAT, locale)
-    }
-    val dateText = yearFormatter.format(time * 1000)
+    val dateText = yearFormatter.get().format(time * 1000)

    return stringRes(context, R.string.last_seen_on_date, dateText, durationText)
 }
@@ -20,6 +20,7 @@
 */
 package com.vitorpamplona.amethyst.ui.note.creators.expiration

+import android.text.format.DateFormat
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
@@ -83,15 +84,14 @@ fun ExpirationDatePicker(model: IExpiration) {
                },
        )

+    val context = LocalContext.current
    val timePickerState =
        rememberTimePickerState(
            initialHour = currentTime.hour,
            initialMinute = currentTime.minute,
-            is24Hour = false,
+            is24Hour = DateFormat.is24HourFormat(context),
        )

-    val context = LocalContext.current
-
    Column(Modifier.fillMaxWidth()) {
        Row(
            verticalAlignment = Alignment.CenterVertically,
@@ -21,6 +21,7 @@
 package com.vitorpamplona.amethyst.ui.note.creators.polls

 import android.annotation.SuppressLint
+import android.text.format.DateFormat
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.fillMaxWidth
@@ -81,15 +82,14 @@ fun PollDeadlinePicker(model: ShortNotePostViewModel) {
                    }
                },
        )
+    val context = LocalContext.current
    val timePickerState =
        rememberTimePickerState(
            initialHour = currentTime.hour,
            initialMinute = currentTime.minute,
-            is24Hour = false, // Set to true if you prefer military time
+            is24Hour = DateFormat.is24HourFormat(context),
        )

-    val context = LocalContext.current
-
    OutlinedCard(
        onClick = { showDatePicker = true },
        modifier = Modifier.fillMaxWidth(),
@@ -21,6 +21,7 @@
 package com.vitorpamplona.amethyst.ui.note.creators.zappolls

 import android.annotation.SuppressLint
+import android.text.format.DateFormat
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.fillMaxWidth
@@ -81,15 +82,14 @@ fun ZapPollDeadlinePicker(model: ShortNotePostViewModel) {
                    }
                },
        )
+    val context = LocalContext.current
    val timePickerState =
        rememberTimePickerState(
            initialHour = currentTime.hour,
            initialMinute = currentTime.minute,
-            is24Hour = false, // Set to true if you prefer military time
+            is24Hour = DateFormat.is24HourFormat(context),
        )

-    val context = LocalContext.current
-
    OutlinedCard(
        onClick = { showDatePicker = true },
        modifier = Modifier.fillMaxWidth(),
@@ -44,6 +44,7 @@ import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clip
 import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.tooling.preview.Preview
 import androidx.compose.ui.unit.dp
@@ -63,6 +64,7 @@ import com.vitorpamplona.amethyst.ui.navigation.navs.INav
 import com.vitorpamplona.amethyst.ui.note.LoadAddressableNote
 import com.vitorpamplona.amethyst.ui.note.NoteCompose
 import com.vitorpamplona.amethyst.ui.note.UserCompose
+import com.vitorpamplona.amethyst.ui.note.formatMediumDate
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.rooms.LoadUser
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.mockAccountViewModel
@@ -76,9 +78,6 @@ import com.vitorpamplona.quartz.experimental.attestations.attestation.tags.Attes
 import com.vitorpamplona.quartz.experimental.attestations.proficiency.AttestorProficiencyEvent
 import com.vitorpamplona.quartz.experimental.attestations.recommendation.AttestorRecommendationEvent
 import com.vitorpamplona.quartz.experimental.attestations.request.AttestationRequestEvent
-import java.text.SimpleDateFormat
-import java.util.Date
-import java.util.Locale

@Preview
@Composable
@@ -188,18 +187,19 @@ fun RenderAttestation(
        }

        if (validFrom != null || validTo != null) {
+            val context = LocalContext.current
            Spacer(modifier = DoubleVertSpacer)
            Row(horizontalArrangement = Arrangement.spacedBy(12.dp)) {
                validFrom?.let {
                    Text(
-                        text = stringRes(R.string.attestation_valid_from, formatTimestamp(it)),
+                        text = stringRes(R.string.attestation_valid_from, formatMediumDate(it, context)),
                        style = MaterialTheme.typography.bodySmall,
                        color = MaterialTheme.colorScheme.onSurfaceVariant,
                    )
                }
                validTo?.let {
                    Text(
-                        text = stringRes(R.string.attestation_valid_to, formatTimestamp(it)),
+                        text = stringRes(R.string.attestation_valid_to, formatMediumDate(it, context)),
                        style = MaterialTheme.typography.bodySmall,
                        color = MaterialTheme.colorScheme.onSurfaceVariant,
                    )
@@ -601,8 +601,3 @@ private fun attestationStatusLabel(status: AttestationStatus?): String =
        status == AttestationStatus.VERIFYING -> stringRes(R.string.attestation_status_verifying)
        else -> stringRes(R.string.attestation)
    }
-
-private fun formatTimestamp(timestamp: Long): String {
-    val sdf = SimpleDateFormat("MMM dd, yyyy", Locale.getDefault())
-    return sdf.format(Date(timestamp * 1000))
-}
@@ -46,6 +46,7 @@ import androidx.compose.runtime.saveable.rememberSaveable
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.style.TextOverflow
 import androidx.compose.ui.unit.dp
@@ -164,6 +165,7 @@ private fun DayRow(
        }

    val startSeconds = view.startSeconds
+    val context = LocalContext.current
    val timeLabel =
        when {
            view.isAllDay -> stringRes(R.string.calendar_all_day)
@@ -172,7 +174,7 @@ private fun DayRow(
                // misleading on day 2 since the event has been ongoing overnight. Show a
                // continuation marker so the user reads it as "still happening".
                stringRes(R.string.calendar_continues)
-            startSeconds != null -> formatTimeOfDay(startSeconds)
+            startSeconds != null -> formatTimeOfDay(startSeconds, context)
            else -> "—"
        }

@@ -72,8 +72,8 @@ fun CalendarEventListCard(
    modifier: Modifier = Modifier,
 ) {
    val view = note.appointmentView() ?: return
-    val range = remember(note.idHex) { formatCalendarRange(note) }
    val context = LocalContext.current
+    val range = remember(note.idHex) { formatCalendarRange(note, context) }
    val relative = remember(note.idHex, view.startSeconds) { relativeTimeLabel(context, view, TimeUtils.now()) }
    val event = note.event ?: return
    val detailRoute =
@@ -20,6 +20,8 @@
 */
 package com.vitorpamplona.amethyst.ui.screen.loggedIn.calendars

+import android.content.Context
+import android.text.format.DateFormat
 import com.vitorpamplona.amethyst.commons.model.nip52Calendar.appointmentView
 import com.vitorpamplona.amethyst.model.Note
 import java.text.SimpleDateFormat
@@ -27,34 +29,73 @@ import java.util.Calendar
 import java.util.Date
 import java.util.Locale

-private val DayMonthFormat = SimpleDateFormat("EEE, MMM d", Locale.getDefault())
-private val FullDateFormat = SimpleDateFormat("EEEE, MMMM d, yyyy", Locale.getDefault())
-private val MonthYearFormat = SimpleDateFormat("MMMM yyyy", Locale.getDefault())
-private val TimeFormat = SimpleDateFormat("h:mm a", Locale.getDefault())
-private val WeekdayShortFormat = SimpleDateFormat("EEE", Locale.getDefault())
+// Skeletons follow Unicode LDML — getBestDateTimePattern picks locale ordering.
+private const val DAY_MONTH_SKELETON = "EEEMMMd" // "Mon, May 28" / "Mon 28 May"
+private const val FULL_DATE_SKELETON = "EEEEMMMMdy" // "Monday, May 28, 2026" / "Monday, 28 May 2026"
+private const val MONTH_YEAR_SKELETON = "MMMMy" // "May 2026" / "Mai 2026"
+private const val WEEKDAY_SHORT_SKELETON = "EEE" // "Mon" — order doesn't matter

-fun formatCalendarRange(note: Note): String? {
+/**
+ * Per-thread cached [SimpleDateFormat] keyed off the current default [Locale].
+ *
+ * Cached because these run per cell in the calendar grid (≈42 cells per month,
+ * 7 per weekday header) — allocating a fresh SimpleDateFormat each call
+ * showed up as scroll-time GC churn. Per-thread because SimpleDateFormat
+ * isn't thread-safe; calendars today are read on the UI thread but future
+ * callers could differ. ThreadLocal gives both — no locks, no contention,
+ * lazy rebuild on locale change.
+ */
+private class LocaleAwareFormatter(
+    private val skeleton: String,
+) {
+    private val cache = ThreadLocal<Pair<Locale, SimpleDateFormat>>()
+
+    fun get(): SimpleDateFormat {
+        val current = Locale.getDefault()
+        val cached = cache.get()
+        if (cached != null && cached.first == current) return cached.second
+        val fresh = SimpleDateFormat(DateFormat.getBestDateTimePattern(current, skeleton), current)
+        cache.set(current to fresh)
+        return fresh
+    }
+}
+
+private val dayMonthFormat = LocaleAwareFormatter(DAY_MONTH_SKELETON)
+private val fullDateFormat = LocaleAwareFormatter(FULL_DATE_SKELETON)
+private val monthYearFormat = LocaleAwareFormatter(MONTH_YEAR_SKELETON)
+private val weekdayShortFormat = LocaleAwareFormatter(WEEKDAY_SHORT_SKELETON)
+
+// Time format respects the user's Android 12/24-hour system setting.
+private fun timeFormat(context: Context): java.text.DateFormat = DateFormat.getTimeFormat(context)
+
+fun formatCalendarRange(
+    note: Note,
+    context: Context,
+): String? {
    val view = note.appointmentView() ?: return null
    val start = view.startSeconds ?: return null
    return if (view.isAllDay) {
        formatDateRange(start, view.endSeconds)
    } else {
-        formatTimeRange(start, view.endSeconds)
+        formatTimeRange(start, view.endSeconds, context)
    }
 }

 private fun formatTimeRange(
    start: Long,
    end: Long?,
+    context: Context,
 ): String {
+    val dayMonth = dayMonthFormat.get()
+    val time = timeFormat(context)
    val startMs = start * 1000
-    val startStr = "${DayMonthFormat.format(Date(startMs))} · ${TimeFormat.format(Date(startMs))}"
+    val startStr = "${dayMonth.format(Date(startMs))} · ${time.format(Date(startMs))}"
    if (end == null || end == start) return startStr
    val endMs = end * 1000
    return if (isSameDay(startMs, endMs)) {
-        "$startStr – ${TimeFormat.format(Date(endMs))}"
+        "$startStr – ${time.format(Date(endMs))}"
    } else {
-        "$startStr – ${DayMonthFormat.format(Date(endMs))} · ${TimeFormat.format(Date(endMs))}"
+        "$startStr – ${dayMonth.format(Date(endMs))} · ${time.format(Date(endMs))}"
    }
 }

@@ -62,12 +103,13 @@ private fun formatDateRange(
    start: Long,
    end: Long?,
 ): String {
-    val startStr = DayMonthFormat.format(Date(start * 1000))
+    val dayMonth = dayMonthFormat.get()
+    val startStr = dayMonth.format(Date(start * 1000))
    if (end == null || end == start) return startStr
-    return "$startStr – ${DayMonthFormat.format(Date(end * 1000))}"
+    return "$startStr – ${dayMonth.format(Date(end * 1000))}"
 }

-fun formatLongDate(unixSeconds: Long): String = FullDateFormat.format(Date(unixSeconds * 1000))
+fun formatLongDate(unixSeconds: Long): String = fullDateFormat.get().format(Date(unixSeconds * 1000))

 fun formatMonthYear(
    year: Int,
@@ -76,10 +118,13 @@ fun formatMonthYear(
    val cal = Calendar.getInstance()
    cal.clear()
    cal.set(year, monthZeroBased, 1)
-    return MonthYearFormat.format(cal.time)
+    return monthYearFormat.get().format(cal.time)
 }

-fun formatTimeOfDay(unixSeconds: Long): String = TimeFormat.format(Date(unixSeconds * 1000))
+fun formatTimeOfDay(
+    unixSeconds: Long,
+    context: Context,
+): String = timeFormat(context).format(Date(unixSeconds * 1000))

 fun formatShortWeekday(weekdayZeroBased: Int): String {
    val cal = Calendar.getInstance()
@@ -87,7 +132,7 @@ fun formatShortWeekday(weekdayZeroBased: Int): String {
    cal.firstDayOfWeek = Calendar.SUNDAY
    cal.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY)
    cal.add(Calendar.DAY_OF_YEAR, weekdayZeroBased)
-    return WeekdayShortFormat.format(cal.time)
+    return weekdayShortFormat.get().format(cal.time)
 }

 private fun isSameDay(
@@ -38,14 +38,15 @@ import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.platform.LocalConfiguration
+import androidx.compose.ui.platform.LocalContext
 import com.vitorpamplona.amethyst.R
 import com.vitorpamplona.amethyst.ui.stringRes
 import java.text.DateFormat
-import java.text.SimpleDateFormat
 import java.time.Instant
 import java.time.ZoneId
 import java.time.ZoneOffset
 import java.util.Date
+import android.text.format.DateFormat as AndroidDateFormat

 /**
 * Tap-to-edit button that opens a Material3 DatePicker (and, when [includeTime] is true,
@@ -68,6 +69,7 @@ fun CalendarDateTimePickerButton(
    var showTime by remember { mutableStateOf(false) }

    val locale = LocalConfiguration.current.locales[0]
+    val context = LocalContext.current
    val pretty =
        if (unixSeconds <= 0L) {
            placeholder
@@ -76,7 +78,7 @@ fun CalendarDateTimePickerButton(
                .getDateTimeInstance(DateFormat.MEDIUM, DateFormat.SHORT, locale)
                .format(Date(unixSeconds * 1000))
        } else {
-            SimpleDateFormat("EEEE, MMMM d, yyyy", locale).format(Date(unixSeconds * 1000))
+            DateFormat.getDateInstance(DateFormat.FULL, locale).format(Date(unixSeconds * 1000))
        }

    val initialMillis = if (unixSeconds > 0L) unixSeconds * 1000L else System.currentTimeMillis()
@@ -94,7 +96,7 @@ fun CalendarDateTimePickerButton(
        rememberTimePickerState(
            initialHour = initialLocal.hour,
            initialMinute = initialLocal.minute,
-            is24Hour = false,
+            is24Hour = AndroidDateFormat.is24HourFormat(context),
        )

    fun reset() {
@@ -318,14 +318,14 @@ private fun EventBody(
                fontWeight = FontWeight.Bold,
            )
        }
-        formatCalendarRange(note)?.let { range ->
+        val context = LocalContext.current
+        formatCalendarRange(note, context)?.let { range ->
            Text(
                text = range,
                style = MaterialTheme.typography.bodyLarge,
                color = MaterialTheme.colorScheme.primary,
            )
        }
-        val context = LocalContext.current
        val relative =
            remember(note.idHex, view.startSeconds) {
                relativeTimeLabel(context, view, TimeUtils.now())
@@ -63,6 +63,7 @@ import com.vitorpamplona.amethyst.ui.screen.loggedIn.nests.room.activity.NestBri
 import com.vitorpamplona.amethyst.ui.stringRes
 import com.vitorpamplona.amethyst.ui.theme.placeholderText
 import kotlinx.coroutines.launch
+import android.text.format.DateFormat as AndroidDateFormat

 /**
 * Bottom sheet that lets the logged-in user start a new NIP-53 kind 30312
@@ -248,6 +249,8 @@ private fun ScheduleStartPicker(
    var showDate by remember { mutableStateOf(false) }
    var showTime by remember { mutableStateOf(false) }

+    val context = LocalContext.current
+
    val pretty =
        if (unixSeconds <= 0L) {
            stringRes(R.string.nest_create_when)
@@ -277,7 +280,7 @@ private fun ScheduleStartPicker(
        androidx.compose.material3.rememberTimePickerState(
            initialHour = initialLocal.hour,
            initialMinute = initialLocal.minute,
-            is24Hour = false,
+            is24Hour = AndroidDateFormat.is24HourFormat(context),
        )

    // On dismiss (Cancel or back-press), restore the picker states
@@ -69,15 +69,13 @@ import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import com.vitorpamplona.amethyst.R
 import com.vitorpamplona.amethyst.ui.navigation.navs.INav
 import com.vitorpamplona.amethyst.ui.navigation.topbars.TopBarWithBackButton
+import com.vitorpamplona.amethyst.ui.note.formatMediumDate
 import com.vitorpamplona.amethyst.ui.note.timeAgoNoDotNoDay
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
 import com.vitorpamplona.amethyst.ui.stringRes
 import com.vitorpamplona.amethyst.ui.theme.ThemeComparisonColumn
 import com.vitorpamplona.amethyst.ui.theme.ThemeComparisonRow
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
-import java.text.SimpleDateFormat
-import java.util.Date
-import java.util.Locale

@Composable
 fun EventSyncScreen(
@@ -750,6 +748,8 @@ private fun DateRangeFilterCard(
    LaunchedEffect(effectiveSince) { onSinceChanged(effectiveSince) }
    LaunchedEffect(effectiveUntil) { onUntilChanged(effectiveUntil) }

+    val context = LocalContext.current
+
    Card(
        modifier =
            Modifier.fillMaxWidth(),
@@ -775,7 +775,7 @@ private fun DateRangeFilterCard(
                        if (effectiveSince == null) {
                            stringRes(R.string.event_sync_date_filter_all_time)
                        } else {
-                            stringRes(R.string.event_sync_date_filter_since) + " " + formatEpochDate(sinceEpoch)
+                            stringRes(R.string.event_sync_date_filter_since) + " " + formatMediumDate(sinceEpoch, context)
                        },
                    style = MaterialTheme.typography.bodySmall,
                    color = MaterialTheme.colorScheme.primary,
@@ -785,7 +785,7 @@ private fun DateRangeFilterCard(
                        if (effectiveUntil == null) {
                            stringRes(R.string.event_sync_date_filter_now)
                        } else {
-                            stringRes(R.string.event_sync_date_filter_until) + " " + formatEpochDate(untilEpoch)
+                            stringRes(R.string.event_sync_date_filter_until) + " " + formatMediumDate(untilEpoch, context)
                        },
                    style = MaterialTheme.typography.bodySmall,
                    color = MaterialTheme.colorScheme.primary,
@@ -810,11 +810,6 @@ private fun DateRangeFilterCard(
    }
 }

-private fun formatEpochDate(epochSecs: Long): String {
-    val sdf = SimpleDateFormat("MMM d, yyyy", Locale.getDefault())
-    return sdf.format(Date(epochSecs * 1000))
-}
-
 // -------------------------------------------------------------------------
 // Helpers
 // -------------------------------------------------------------------------
@@ -20,6 +20,7 @@
 */
 package com.vitorpamplona.amethyst.ui.screen.loggedIn.relays.vanish

+import android.text.format.DateFormat
 import androidx.compose.foundation.border
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
@@ -58,6 +59,7 @@ import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.tooling.preview.Preview
@@ -72,6 +74,7 @@ import com.vitorpamplona.amethyst.ui.components.TitleExplainer
 import com.vitorpamplona.amethyst.ui.navigation.navs.EmptyNav
 import com.vitorpamplona.amethyst.ui.navigation.navs.INav
 import com.vitorpamplona.amethyst.ui.navigation.topbars.TopBarWithBackButton
+import com.vitorpamplona.amethyst.ui.note.formatMediumDateTime
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.mockAccountViewModel
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.relays.common.BasicRelaySetupInfoDialog
@@ -85,12 +88,9 @@ import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.displayUrl
 import com.vitorpamplona.quartz.utils.TimeUtils
 import kotlinx.collections.immutable.toImmutableList
-import java.text.SimpleDateFormat
 import java.time.Instant
 import java.time.ZoneId
 import java.time.ZoneOffset
-import java.util.Date
-import java.util.Locale

@OptIn(ExperimentalMaterial3Api::class)
@Composable
@@ -131,11 +131,12 @@ fun RequestToVanishScreen(

    val currentTime = Instant.ofEpochMilli(vanishDate * 1000).atZone(ZoneId.systemDefault()).toLocalDateTime()

+    val context = LocalContext.current
    val timePickerState =
        rememberTimePickerState(
            initialHour = currentTime.hour,
            initialMinute = currentTime.minute,
-            is24Hour = false,
+            is24Hour = DateFormat.is24HourFormat(context),
        )

    val relayOptions =
@@ -288,7 +289,7 @@ fun RequestToVanishScreen(
                    )
                    Spacer(Modifier.width(12.dp))
                    Text(
-                        text = formatTimestamp(vanishDate),
+                        text = formatMediumDateTime(vanishDate, context),
                        style = MaterialTheme.typography.bodyLarge,
                    )
                }
@@ -461,11 +462,6 @@ private fun ConfirmVanishDialog(
    )
 }

-private fun formatTimestamp(epochSeconds: Long): String {
-    val sdf = SimpleDateFormat("MMM dd, yyyy  hh:mm a", Locale.getDefault())
-    return sdf.format(Date(epochSeconds * 1000))
-}
-
@Preview
@Composable
 fun RequestToVanishScreenPreview() {
@@ -47,6 +47,7 @@ import androidx.compose.runtime.getValue
 import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.style.TextOverflow
 import androidx.compose.ui.unit.dp
@@ -58,15 +59,13 @@ import com.vitorpamplona.amethyst.model.nip62Vanish.ComplianceStatus
 import com.vitorpamplona.amethyst.model.nip62Vanish.VanishEventItem
 import com.vitorpamplona.amethyst.ui.navigation.navs.INav
 import com.vitorpamplona.amethyst.ui.navigation.topbars.TopBarWithBackButton
+import com.vitorpamplona.amethyst.ui.note.formatMediumDateTime
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
 import com.vitorpamplona.amethyst.ui.stringRes
 import com.vitorpamplona.amethyst.ui.theme.DividerThickness
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.displayUrl
 import kotlinx.coroutines.launch
-import java.text.SimpleDateFormat
-import java.util.Date
-import java.util.Locale

@Composable
 fun VanishEventsScreen(
@@ -170,6 +169,7 @@ private fun VanishEventCard(
                containerColor = MaterialTheme.colorScheme.surfaceContainerLow,
            ),
    ) {
+        val context = LocalContext.current
        Column(modifier = Modifier.padding(16.dp)) {
            Row(
                modifier = Modifier.fillMaxWidth(),
@@ -182,7 +182,7 @@ private fun VanishEventCard(
                    color = MaterialTheme.colorScheme.onSurfaceVariant,
                )
                Text(
-                    text = formatTimestamp(item.event.createdAt),
+                    text = formatMediumDateTime(item.event.createdAt, context),
                    style = MaterialTheme.typography.bodyMedium,
                    fontWeight = FontWeight.SemiBold,
                )
@@ -355,8 +355,3 @@ private fun RelayComplianceRow(
        }
    }
 }
-
-private fun formatTimestamp(epochSeconds: Long): String {
-    val sdf = SimpleDateFormat("MMM dd, yyyy  hh:mm a", Locale.getDefault())
-    return sdf.format(Date(epochSeconds * 1000))
-}
@@ -60,6 +60,7 @@ import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.platform.LocalSoftwareKeyboardController
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.text.font.FontFamily
@@ -72,6 +73,7 @@ import com.vitorpamplona.amethyst.R
 import com.vitorpamplona.amethyst.commons.icons.symbols.Icon
 import com.vitorpamplona.amethyst.commons.icons.symbols.MaterialSymbols
 import com.vitorpamplona.amethyst.commons.model.nip05DnsIdentifiers.namecoin.NamecoinSettings
+import com.vitorpamplona.amethyst.ui.note.formatMediumDateTime
 import com.vitorpamplona.quartz.nip05DnsIdentifiers.namecoin.DEFAULT_ELECTRUMX_SERVERS
 import com.vitorpamplona.quartz.nip05DnsIdentifiers.namecoin.ElectrumxServer
 import com.vitorpamplona.quartz.nip05DnsIdentifiers.namecoin.NamecoinBackend
@@ -79,8 +81,6 @@ import com.vitorpamplona.quartz.nip05DnsIdentifiers.namecoin.NamecoinCoreRpcConf
 import com.vitorpamplona.quartz.nip05DnsIdentifiers.namecoin.RpcProbeResult
 import com.vitorpamplona.quartz.nip05DnsIdentifiers.namecoin.ServerTestResult
 import kotlinx.coroutines.launch
-import java.text.SimpleDateFormat
-import java.util.Date
 import java.util.Locale

 /**
@@ -497,10 +497,10 @@ private fun DiagnosticCard(

            // Last test timestamp
            if (lastTestTimestamp != null) {
+                val context = LocalContext.current
                val formatted =
-                    remember(lastTestTimestamp) {
-                        SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.getDefault())
-                            .format(Date(lastTestTimestamp))
+                    remember(lastTestTimestamp, context) {
+                        formatMediumDateTime(lastTestTimestamp / 1000L, context)
                    }
                val successCount = testResults.count { it.success }
                val totalCount = testResults.size
@@ -51,6 +51,7 @@ import androidx.compose.runtime.getValue
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.platform.LocalUriHandler
 import androidx.compose.ui.platform.UriHandler
 import androidx.compose.ui.text.font.FontFamily
@@ -65,15 +66,13 @@ import com.vitorpamplona.amethyst.ui.navigation.navs.INav
 import com.vitorpamplona.amethyst.ui.navigation.routes.Route
 import com.vitorpamplona.amethyst.ui.note.UserPicture
 import com.vitorpamplona.amethyst.ui.note.UsernameDisplay
+import com.vitorpamplona.amethyst.ui.note.formatMonthDayTime
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.rooms.LoadUser
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.wallet.datasource.OnchainZapsFilterAssemblerSubscription
 import com.vitorpamplona.amethyst.ui.stringRes
 import com.vitorpamplona.amethyst.ui.theme.bitcoinColor
 import java.text.NumberFormat
-import java.text.SimpleDateFormat
-import java.util.Date
-import java.util.Locale
 import kotlin.math.absoluteValue

@OptIn(ExperimentalMaterial3Api::class)
@@ -299,14 +298,11 @@ private fun OnchainTransactionItem(
            (if (isIncoming) "+" else "-") + fmt.format(amountSats)
        }

+    val context = LocalContext.current
    val dateText =
-        remember(view.tx.blockTime, view.tx.confirmations) {
+        remember(view.tx.blockTime, view.tx.confirmations, context) {
            val ts = view.tx.blockTime
-            if (ts != null) {
-                SimpleDateFormat("MMM d, HH:mm", Locale.getDefault()).format(Date(ts * 1000L))
-            } else {
-                ""
-            }
+            if (ts != null) formatMonthDayTime(ts, context) else ""
        }

    val counterpartyPubkeyHex = view.counterpartyPubkeyHex()
@@ -50,6 +50,7 @@ import androidx.compose.runtime.getValue
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
+import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.style.TextOverflow
 import androidx.compose.ui.unit.dp
@@ -60,15 +61,13 @@ import com.vitorpamplona.amethyst.commons.icons.symbols.MaterialSymbols
 import com.vitorpamplona.amethyst.ui.navigation.navs.INav
 import com.vitorpamplona.amethyst.ui.note.UserPicture
 import com.vitorpamplona.amethyst.ui.note.UsernameDisplay
+import com.vitorpamplona.amethyst.ui.note.formatMonthDayTime
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.AccountViewModel
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.chats.rooms.LoadUser
 import com.vitorpamplona.amethyst.ui.stringRes
 import com.vitorpamplona.quartz.nip47WalletConnect.rpc.NwcTransaction
 import com.vitorpamplona.quartz.nip47WalletConnect.rpc.NwcTransactionType
 import java.text.NumberFormat
-import java.text.SimpleDateFormat
-import java.util.Date
-import java.util.Locale

@OptIn(ExperimentalMaterial3Api::class)
@Composable
@@ -238,12 +237,10 @@ private fun TransactionItem(
            (if (isIncoming) "+" else "-") + fmt.format(amountSats)
        }

+    val context = LocalContext.current
    val dateText =
-        remember(tx.created_at) {
-            tx.created_at?.let {
-                val sdf = SimpleDateFormat("MMM d, HH:mm", Locale.getDefault())
-                sdf.format(Date(it * 1000L))
-            } ?: ""
+        remember(tx.created_at, context) {
+            tx.created_at?.let { formatMonthDayTime(it, context) } ?: ""
        }

    val parsed = remember(tx.metadata) { tx.parsedMetadata() }
@@ -27,23 +27,39 @@ import java.util.Calendar
 import java.util.Date
 import java.util.Locale

-private const val YEAR_DATE_FORMAT = "MMM dd, yyyy"
-private const val MONTH_DATE_FORMAT = "MMM dd"
+// Month + day without year — month name is textual so order is unambiguous across locales.
+private const val MONTH_DATE_FORMAT = "MMM d"

-private var locale = Locale.getDefault()
-private var yearFormatter = SimpleDateFormat(YEAR_DATE_FORMAT, locale)
-private var monthFormatter = SimpleDateFormat(MONTH_DATE_FORMAT, locale)
-private var timeOnlyFormatter = DateFormat.getTimeInstance(DateFormat.SHORT, locale)
+/**
+ * Per-thread cached [DateFormat] keyed off the current default [Locale].
+ *
+ * `DateFormat`/`SimpleDateFormat` are mutable and not thread-safe. These
+ * formatters can be read from UI threads (composition) and from background
+ * coroutines. `ThreadLocal` gives each thread its own instance — no locks,
+ * no allocation per call, and we rebuild lazily on locale change.
+ */
+private class LocaleAwareFormatter(
+    private val build: (Locale) -> DateFormat,
+) {
+    private val cache = ThreadLocal<Pair<Locale, DateFormat>>()

-private fun updateFormattersIfNeeded() {
-    if (locale != Locale.getDefault()) {
-        locale = Locale.getDefault()
-        yearFormatter = SimpleDateFormat(YEAR_DATE_FORMAT, locale)
-        monthFormatter = SimpleDateFormat(MONTH_DATE_FORMAT, locale)
-        timeOnlyFormatter = DateFormat.getTimeInstance(DateFormat.SHORT, locale)
+    fun get(): DateFormat {
+        val current = Locale.getDefault()
+        val cached = cache.get()
+        if (cached != null && cached.first == current) return cached.second
+        val fresh = build(current)
+        cache.set(current to fresh)
+        return fresh
    }
 }

+// Locale-aware: en-US "May 28, 2026" · en-GB "28 May 2026" · de-DE "28.05.2026" · ja-JP "2026/05/28"
+private val yearFormatter = LocaleAwareFormatter { DateFormat.getDateInstance(DateFormat.MEDIUM, it) }
+private val monthFormatter = LocaleAwareFormatter { SimpleDateFormat(MONTH_DATE_FORMAT, it) }
+
+// Locale-aware: en-US "2:32 PM" · en-GB "14:32" · de-DE "14:32"
+private val timeOnlyFormatter = LocaleAwareFormatter { DateFormat.getTimeInstance(DateFormat.SHORT, it) }
+
 /**
 * Formats a Unix timestamp (seconds) as a human-readable time ago string.
 * Returns strings like " • 5m", " • 2h", " • Dec 12"
@@ -64,13 +80,11 @@ fun timeAgo(

    return when {
        timeDifference > TimeUtils.ONE_YEAR -> {
-            updateFormattersIfNeeded()
-            prefix + yearFormatter.format(time * 1000)
+            prefix + yearFormatter.get().format(time * 1000)
        }

        timeDifference > TimeUtils.ONE_MONTH -> {
-            updateFormattersIfNeeded()
-            prefix + monthFormatter.format(time * 1000)
+            prefix + monthFormatter.get().format(time * 1000)
        }

        timeDifference > TimeUtils.ONE_DAY -> {
@@ -131,13 +145,11 @@ fun dateFormatter(

    return when {
        timeDifference > TimeUtils.ONE_YEAR -> {
-            updateFormattersIfNeeded()
-            yearFormatter.format(time * 1000)
+            yearFormatter.get().format(time * 1000)
        }

        timeDifference > TimeUtils.ONE_DAY -> {
-            updateFormattersIfNeeded()
-            monthFormatter.format(time * 1000)
+            monthFormatter.get().format(time * 1000)
        }

        else -> {
@@ -154,9 +166,9 @@ fun Long.toTimeAgo(withDot: Boolean = true): String = timeAgo(this, withDot)
 /**
 * Formats a Unix timestamp (seconds) as an absolute date/time string. Granularity
 * depends on how far in the past the timestamp is:
- *   - same day → time only (e.g. "14:32"), locale-aware
- *   - same year → "MMM dd, HH:mm"
- *   - older    → "MMM dd, yyyy"
+ *   - same day → locale-aware short time (e.g. "14:32" / "2:32 PM")
+ *   - same year → month + day + short time (e.g. "May 28, 2:32 PM")
+ *   - older    → locale-aware medium date (e.g. "May 28, 2026" / "28 May 2026" / "28.05.2026")
 */
 fun timeAbsolute(
    time: Long?,
@@ -167,8 +179,6 @@ fun timeAbsolute(
    val prefix = if (withDot) " • " else ""
    if (time == 0L) return prefix + never

-    updateFormattersIfNeeded()
-
    val timeMs = time * 1000
    val now = Calendar.getInstance()
    val then = Calendar.getInstance().apply { timeInMillis = timeMs }
@@ -176,12 +186,12 @@ fun timeAbsolute(
    val sameYear = now.get(Calendar.YEAR) == then.get(Calendar.YEAR)
    val sameDay = sameYear && now.get(Calendar.DAY_OF_YEAR) == then.get(Calendar.DAY_OF_YEAR)

-    val timeOfDay = timeOnlyFormatter.format(Date(timeMs))
+    val timeOfDay = timeOnlyFormatter.get().format(Date(timeMs))

    return when {
        sameDay -> prefix + timeOfDay
-        sameYear -> prefix + monthFormatter.format(timeMs) + ", " + timeOfDay
-        else -> prefix + yearFormatter.format(timeMs)
+        sameYear -> prefix + monthFormatter.get().format(timeMs) + ", " + timeOfDay
+        else -> prefix + yearFormatter.get().format(timeMs)
    }
 }

@@ -97,12 +97,12 @@ import com.vitorpamplona.quartz.nip47WalletConnect.Nip47WalletConnect
 import com.vitorpamplona.quartz.nip51Lists.bookmarkList.BookmarkListEvent
 import com.vitorpamplona.quartz.nip57Zaps.LnZapEvent
 import kotlinx.coroutines.launch
-import java.time.Instant
-import java.time.ZoneId
-import java.time.format.DateTimeFormatter
+import java.text.DateFormat
+import java.util.Date
 import java.util.Locale

-private val articleDateFormat = DateTimeFormatter.ofPattern("MMM d, yyyy", Locale.getDefault())
+// Locale-aware: en-US "May 28, 2026" · en-GB "28 May 2026" · de-DE "28.05.2026" · ja-JP "2026/05/28"
+private val articleDateFormat = DateFormat.getDateInstance(DateFormat.MEDIUM, Locale.getDefault())

 /**
 * Parses a NIP-23 address tag in the format "30023:pubkey:d-tag".
@@ -352,11 +352,7 @@ fun ArticleReaderScreen(
    val publishedAt =
        article?.let { art ->
            val ts = art.publishedAt() ?: art.createdAt
-            Instant
-                .ofEpochSecond(ts)
-                .atZone(ZoneId.systemDefault())
-                .toLocalDate()
-                .format(articleDateFormat)
+            articleDateFormat.format(Date(ts * 1000L))
        }

    // Author info from local cache
@@ -69,19 +69,14 @@ import com.vitorpamplona.amethyst.desktop.subscriptions.rememberSubscription
 import com.vitorpamplona.quartz.nip02FollowList.ContactListEvent
 import com.vitorpamplona.quartz.nip23LongContent.LongTextNoteEvent
 import com.vitorpamplona.quartz.nip47WalletConnect.Nip47WalletConnect
-import java.time.Instant
-import java.time.ZoneId
-import java.time.format.DateTimeFormatter
+import java.text.DateFormat
+import java.util.Date
 import java.util.Locale

-private val dateFormat = DateTimeFormatter.ofPattern("MMM d, yyyy", Locale.getDefault())
+// Locale-aware: en-US "May 28, 2026" · en-GB "28 May 2026" · de-DE "28.05.2026" · ja-JP "2026/05/28"
+private val dateFormat = DateFormat.getDateInstance(DateFormat.MEDIUM, Locale.getDefault())

-private fun formatDate(timestamp: Long): String =
-    Instant
-        .ofEpochSecond(timestamp)
-        .atZone(ZoneId.systemDefault())
-        .toLocalDate()
-        .format(dateFormat)
+private fun formatDate(timestamp: Long): String = dateFormat.format(Date(timestamp * 1000L))

 /**
 * Card displaying long-form content (NIP-23) with title, summary, and image.
@@ -59,9 +59,9 @@ import com.vitorpamplona.amethyst.commons.model.highlights.HighlightData
 import com.vitorpamplona.amethyst.commons.ui.components.EmptyState
 import com.vitorpamplona.amethyst.desktop.service.highlights.DesktopHighlightStore
 import kotlinx.coroutines.launch
-import java.time.Instant
-import java.time.ZoneId
-import java.time.format.DateTimeFormatter
+import java.text.DateFormat
+import java.util.Date
+import java.util.Locale

@Composable
 fun MyHighlightsScreen(
@@ -238,8 +238,8 @@ private fun HighlightCard(
    }
 }

-private fun formatTimestamp(epochSeconds: Long): String =
-    Instant
-        .ofEpochSecond(epochSeconds)
-        .atZone(ZoneId.systemDefault())
-        .format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm"))
+// Locale-aware date+time, e.g. en-US "May 28, 2026 2:32 PM" · de-DE "28.05.2026 14:32".
+private val dateTimeFormat =
+    DateFormat.getDateTimeInstance(DateFormat.MEDIUM, DateFormat.SHORT, Locale.getDefault())
+
+private fun formatTimestamp(epochSeconds: Long): String = dateTimeFormat.format(Date(epochSeconds * 1000L))