diff --git a/app/static/js/app.js b/app/static/js/app.js
index 016f957..f1e48d3 100644
--- a/app/static/js/app.js
+++ b/app/static/js/app.js
@@ -4591,45 +4591,14 @@ function scrollToBottom() {
 }
 
 /**
- * Format timestamp
+ * Format a message timestamp.
+ * Archive views always show the full date, since "Today" is meaningless there.
  */
 function formatTime(timestamp) {
-    const date = new Date(timestamp * 1000);
-
-    // When viewing archive, always show full date + time
-    if (currentArchiveDate) {
-        return date.toLocaleDateString() + ' ' + date.toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' });
-    }
-
-    // When viewing live messages, compare calendar dates
-    const now = new Date();
-    const yesterday = new Date(now);
-    yesterday.setDate(yesterday.getDate() - 1);
-
-    if (date.toDateString() === now.toDateString()) {
-        // Today - show time only
-        return date.toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' });
-    } else if (date.toDateString() === yesterday.toDateString()) {
-        // Yesterday
-        return 'Yesterday ' + date.toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' });
-    } else {
-        // Older - show date and time
-        return date.toLocaleDateString() + ' ' + date.toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' });
-    }
+    return formatTimestamp(timestamp, { absolute: !!currentArchiveDate });
 }
 
-/**
- * Format a unix timestamp as relative time (e.g., "5 min ago", "2h ago")
- */
-function formatTimeAgo(timestamp) {
-    const now = Math.floor(Date.now() / 1000);
-    const diff = now - timestamp;
-    if (diff < 60) return 'just now';
-    if (diff < 3600) return `${Math.floor(diff / 60)} min ago`;
-    if (diff < 86400) return `${Math.floor(diff / 3600)}h ago`;
-    if (diff < 604800) return `${Math.floor(diff / 86400)}d ago`;
-    return new Date(timestamp * 1000).toLocaleDateString();
-}
+// formatTimeAgo() comes from datetime-utils.js.
 
 /**
  * Update character counter (counts UTF-8 bytes, not characters)
diff --git a/app/static/js/datetime-utils.js b/app/static/js/datetime-utils.js
new file mode 100644
index 0000000..59815df
--- /dev/null
+++ b/app/static/js/datetime-utils.js
@@ -0,0 +1,81 @@
+/**
+ * Shared date/time and number formatting.
+ *
+ * Policy: numeric formatting follows the BROWSER locale, only the words are translated.
+ *
+ * That split is deliberate. Tying the clock to the UI language would flip a Polish
+ * operator to "09:53 AM" the moment they switched the interface to English, and mesh
+ * operators want 24-hour time regardless of what language the menus are in. The browser
+ * locale already reflects how the user wants dates and numbers written, so leave it
+ * alone and translate only "Yesterday", "just now" and friends.
+ *
+ * Loaded via _head_i18n.html on every page, after the translation runtime.
+ */
+
+/** HH:MM in the browser's locale. */
+function formatClock(date) {
+    return date.toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' });
+}
+
+/**
+ * Format a unix timestamp as today / yesterday / an older date.
+ *
+ * @param {number} timestamp - unix seconds
+ * @param {Object} [opts]
+ * @param {boolean} [opts.absolute] - always show the full date, never today/yesterday
+ * @param {'full'|'short'} [opts.dateStyle] - how older dates are written
+ * @returns {string}
+ */
+function formatTimestamp(timestamp, opts) {
+    if (!timestamp) return '';
+    const { absolute = false, dateStyle = 'full' } = opts || {};
+
+    const date = new Date(timestamp * 1000);
+    const longDate = () => (dateStyle === 'short'
+        ? date.toLocaleDateString([], { month: 'short', day: 'numeric' })
+        : date.toLocaleDateString());
+
+    if (absolute) return `${longDate()} ${formatClock(date)}`;
+
+    const now = new Date();
+    const yesterday = new Date(now);
+    yesterday.setDate(yesterday.getDate() - 1);
+
+    if (date.toDateString() === now.toDateString()) {
+        return formatClock(date);
+    }
+    if (date.toDateString() === yesterday.toDateString()) {
+        return `${t('common.yesterday')} ${formatClock(date)}`;
+    }
+    return `${longDate()} ${formatClock(date)}`;
+}
+
+/**
+ * Format a unix timestamp as relative time ("5 min ago", "2h ago").
+ * @param {number} timestamp - unix seconds
+ * @returns {string}
+ */
+function formatTimeAgo(timestamp) {
+    const diff = Math.floor(Date.now() / 1000) - timestamp;
+
+    if (diff < 60) return t('common.just_now');
+    if (diff < 3600) return t('common.minutes_ago', { count: Math.floor(diff / 60) });
+    if (diff < 86400) return t('common.hours_ago', { count: Math.floor(diff / 3600) });
+    if (diff < 604800) return tn('common.days_ago', Math.floor(diff / 86400));
+    return new Date(timestamp * 1000).toLocaleDateString();
+}
+
+/**
+ * Thousands-separated integer in the browser's locale, em dash for missing values.
+ * @param {number|null} n
+ * @returns {string}
+ */
+function formatInt(n) {
+    if (n == null || isNaN(n)) return '—';
+    return Number(n).toLocaleString();
+}
+
+window.formatClock = formatClock;
+window.formatTimestamp = formatTimestamp;
+window.formatTimeAgo = formatTimeAgo;
+window.formatInt = formatInt;
diff --git a/app/static/js/dm.js b/app/static/js/dm.js
index b357f7a..55b6556 100644
--- a/app/static/js/dm.js
+++ b/app/static/js/dm.js
@@ -1783,24 +1783,11 @@ function updateLastRefresh() {
 }
 
 /**
- * Format timestamp to readable time
+ * Format timestamp to readable time.
+ * Uses the short date form ("5 Aug") — DM rows are narrower than channel messages.
  */
 function formatTime(timestamp) {
-    if (!timestamp) return '';
-
-    const date = new Date(timestamp * 1000);
-    const now = new Date();
-    const yesterday = new Date(now);
-    yesterday.setDate(yesterday.getDate() - 1);
-
-    if (date.toDateString() === now.toDateString()) {
-        return date.toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' });
-    } else if (date.toDateString() === yesterday.toDateString()) {
-        return 'Yesterday ' + date.toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' });
-    } else {
-        return date.toLocaleDateString([], { month: 'short', day: 'numeric' }) +
-               ' ' + date.toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' });
-    }
+    return formatTimestamp(timestamp, { dateStyle: 'short' });
 }
 
 /**
diff --git a/app/static/js/repeater-manage.js b/app/static/js/repeater-manage.js
index e75257e..6f84e7a 100644
--- a/app/static/js/repeater-manage.js
+++ b/app/static/js/repeater-manage.js
@@ -278,9 +278,11 @@ function fmtDuration(seconds) {
     return parts.join(' ');
 }
 
+// Delegates to datetime-utils.js; no longer forces en-US thousands separators, so
+// numbers follow the reader's locale. Kept as a declaration (not const) so it stays
+// hoisted, like the implementation it replaced.
 function fmtInt(n) {
-    if (n == null || isNaN(n)) return '—';
-    return Number(n).toLocaleString('en-US');
+    return formatInt(n);
 }
 
 function batteryPercent(mv) {
diff --git a/app/static/js/sw.js b/app/static/js/sw.js
index ca6ebad..99a5c50 100644
--- a/app/static/js/sw.js
+++ b/app/static/js/sw.js
@@ -8,6 +8,7 @@ const ASSETS_TO_CACHE = [
     '/static/js/message-utils.js',
     '/static/js/filter-utils.js',
     '/static/js/i18n-runtime.js',
+    '/static/js/datetime-utils.js',
     '/static/js/console.js',
     '/static/images/android-chrome-192x192.png',
     '/static/images/android-chrome-512x512.png',
diff --git a/app/templates/_head_i18n.html b/app/templates/_head_i18n.html
index 0cfc7cd..6219595 100644
--- a/app/templates/_head_i18n.html
+++ b/app/templates/_head_i18n.html
@@ -8,3 +8,4 @@
    (including the 6 iframes) share a single cached fetch. #}
 <script src="{{ i18n_catalog_url }}"></script>
 <script src="{{ url_for('static', filename='js/i18n-runtime.js') }}"></script>
+<script src="{{ url_for('static', filename='js/datetime-utils.js') }}"></script>
diff --git a/app/translations/en.json b/app/translations/en.json
index f11dbee..fc55f5d 100644
--- a/app/translations/en.json
+++ b/app/translations/en.json
@@ -1,4 +1,13 @@
 {
+  "common.days_ago": {
+    "one": "{count}d ago",
+    "other": "{count}d ago"
+  },
+  "common.hours_ago": "{count}h ago",
+  "common.just_now": "just now",
+  "common.minutes_ago": "{count} min ago",
+  "common.yesterday": "Yesterday",
+
   "meta.language_english_name": "English",
   "meta.language_name": "English",
   "meta.translator": "mc-webui"
diff --git a/app/translations/pl.json b/app/translations/pl.json
index 3e12af8..9d76015 100644
--- a/app/translations/pl.json
+++ b/app/translations/pl.json
@@ -1,4 +1,15 @@
 {
+  "common.days_ago": {
+    "one": "{count} dzień temu",
+    "few": "{count} dni temu",
+    "many": "{count} dni temu",
+    "other": "{count} dnia temu"
+  },
+  "common.hours_ago": "{count} godz. temu",
+  "common.just_now": "przed chwilą",
+  "common.minutes_ago": "{count} min temu",
+  "common.yesterday": "Wczoraj",
+
   "meta.language_english_name": "Polish",
   "meta.language_name": "Polski",
   "meta.translator": "mc-webui"