Index: binaries/data/mods/public/gui/civinfo/civinfo.xml
===================================================================
--- binaries/data/mods/public/gui/civinfo/civinfo.xml
+++ binaries/data/mods/public/gui/civinfo/civinfo.xml
@@ -2,6 +2,7 @@
 
 <objects>
 
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/common/functions_civinfo.js"/>
 	<script file="gui/common/functions_global_object.js"/>
 	<script file="gui/common/functions_utility.js"/>
Index: binaries/data/mods/public/gui/common/functions_global_object.js
===================================================================
--- binaries/data/mods/public/gui/common/functions_global_object.js
+++ binaries/data/mods/public/gui/common/functions_global_object.js
@@ -70,7 +70,7 @@
 		counters.push(sprintf(translate("FPS: %(fps)4s"), { "fps": Engine.GetFPS() }));
 
 	if (Engine.ConfigDB_GetValue("user", "overlay.realtime") === "true")
-		counters.push((new Date()).toLocaleTimeString());
+		counters.push(timeOfDayToString(Date.now()));
 
 	// If game has been started
 	if (typeof appendSessionCounters != "undefined")
Index: binaries/data/mods/public/gui/common/functions_utility.js
===================================================================
--- binaries/data/mods/public/gui/common/functions_utility.js
+++ binaries/data/mods/public/gui/common/functions_utility.js
@@ -108,15 +108,10 @@
 	return mapTitle == "random" ? translateWithContext("map selection", "Random") : translate(mapTitle);
 }
 
-/**
- * Convert time in milliseconds to [hh:]mm:ss string representation.
- * @param time Time period in milliseconds (integer)
- * @return String representing time period
- */
-function timeToString(time)
+function chatTimestampToString(time)
 {
-	return Engine.FormatMillisecondsIntoDateStringGMT(time, time < 1000 * 60 * 60 ?
-		translate("mm:ss") : translate("HH:mm:ss"));
+	// Translation: Time prefix as shown in the chat in the lobby, game setup, and session.
+	return sprintf(translate("\\[%(time)s]"), { "time": timeOfDayToString(time) });
 }
 
 function removeDupes(array)
Index: binaries/data/mods/public/gui/common/functions_utility_loadsave.js
===================================================================
--- binaries/data/mods/public/gui/common/functions_utility_loadsave.js
+++ binaries/data/mods/public/gui/common/functions_utility_loadsave.js
@@ -11,9 +11,7 @@
 
 function generateSavegameDateString(metadata, engineInfo)
 {
-	return compatibilityColor(
-		Engine.FormatMillisecondsIntoDateStringLocal(metadata.time * 1000, translate("yyyy-MM-dd HH:mm:ss")),
-		isCompatibleSavegame(metadata, engineInfo));
+	return compatibilityColor(datetimeToString(metadata.time * 1000), isCompatibleSavegame(metadata, engineInfo));
 }
 
 function generateSavegameLabel(metadata, engineInfo)
Index: binaries/data/mods/public/gui/common/l10n.js
===================================================================
--- binaries/data/mods/public/gui/common/l10n.js
+++ binaries/data/mods/public/gui/common/l10n.js
@@ -0,0 +1,41 @@
+function durationToString(time)
+{
+	return Engine.FormatMillisecondsIntoDateStringGMT(time, time < 1000 * 60 * 60 ?
+		// Translation: Format of the time elapsed or remaining, for game durations, ceasefire and wonder-victory countdowns, etc.
+		// For a list of symbols that you can use, see:
+		// https://sites.google.com/site/icuprojectuserguide/formatparse/datetime?pli=1#TOC-Date-Field-Symbol-Table
+		// The default format is for the US, but every language/country will probably use this format too.
+		translateWithContext("duration less than one hour", "m:ss") :
+		// Translation: Format of the time elapsed or remaining, for game durations, ceasefire and wonder-victory countdowns, etc.
+		// For a list of symbols that you can use, see:
+		// https://sites.google.com/site/icuprojectuserguide/formatparse/datetime?pli=1#TOC-Date-Field-Symbol-Table
+		// The default format is for the US, but every language/country will probably use this format too.
+		translateWithContext("duration greater than one hour", "H:mm:ss"));
+}
+
+function timeOfDayToString(time)
+{
+	// Translation: Format of the local time as shown in the chat in the lobby, game setup, and session, and the lobby game start time.
+	// For a list of symbols that you can use, see:
+	// https://sites.google.com/site/icuprojectuserguide/formatparse/datetime?pli=1#TOC-Date-Field-Symbol-Table
+	// The default format is for the US. Most other languages/countries may want to use "HH:mm" instead.
+	return Engine.FormatMillisecondsIntoDateStringLocal(time, translateWithContext("time of day", "h:mm a"));
+}
+
+function datetimeToString(datetime)
+{
+	// Translation: Format of the local datetime as shown in the load game, save game, and replay menus.
+	// For a list of symbols that you can use, see:
+	// https://sites.google.com/site/icuprojectuserguide/formatparse/datetime?pli=1#TOC-Date-Field-Symbol-Table
+	// The default format is for the US. Most other languages/countries may want to use "yyyy-MM-dd HH:mm" instead.
+	return Engine.FormatMillisecondsIntoDateStringLocal(datetime, translateWithContext("datetime", "M/d/yyyy h:mm a"));
+}
+
+function monthToString(datetime)
+{
+	// Translation: Format of the local date (month) as shown in the date filter dropdown in the replay menu.
+	// For a list of symbols that you can use, see:
+	// https://sites.google.com/site/icuprojectuserguide/formatparse/datetime?pli=1#TOC-Date-Field-Symbol-Table
+	// The default format is for the US. Most other languages/countries may want to use "yyyy-MM" instead.
+	return Engine.FormatMillisecondsIntoDateStringLocal(datetime, translateWithContext("date month", "M/yyyy"));
+}
Index: binaries/data/mods/public/gui/credits/credits.xml
===================================================================
--- binaries/data/mods/public/gui/credits/credits.xml
+++ binaries/data/mods/public/gui/credits/credits.xml
@@ -7,6 +7,7 @@
 -->
 
 <objects>
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/common/functions_global_object.js"/>
 	<script directory="gui/credits/"/>
 
Index: binaries/data/mods/public/gui/gamesetup/gamesetup.js
===================================================================
--- binaries/data/mods/public/gui/gamesetup/gamesetup.js
+++ binaries/data/mods/public/gui/gamesetup/gamesetup.js
@@ -2249,9 +2249,7 @@
 
 	if (Engine.ConfigDB_GetValue("user", "chat.timestamp") == "true")
 		text = sprintf(translate("%(time)s %(message)s"), {
-			"time": sprintf(translate("\\[%(time)s]"), {
-				"time": Engine.FormatMillisecondsIntoDateStringLocal(Date.now(), translate("HH:mm"))
-			}),
+			"time": chatTimestampToString(Date.now()),
 			"message": text
 		});
 
Index: binaries/data/mods/public/gui/gamesetup/gamesetup.xml
===================================================================
--- binaries/data/mods/public/gui/gamesetup/gamesetup.xml
+++ binaries/data/mods/public/gui/gamesetup/gamesetup.xml
@@ -2,6 +2,7 @@
 
 <objects>
 
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/common/color.js"/>
 	<script file="gui/common/functions_civinfo.js"/>
 	<script file="gui/common/functions_global_object.js"/>
Index: binaries/data/mods/public/gui/gamesetup_mp/gamesetup_mp.xml
===================================================================
--- binaries/data/mods/public/gui/gamesetup_mp/gamesetup_mp.xml
+++ binaries/data/mods/public/gui/gamesetup_mp/gamesetup_mp.xml
@@ -2,6 +2,7 @@
 
 <objects>
 
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/common/network.js"/>
 	<script file="gui/common/functions_global_object.js"/>
 	<script file="gui/common/functions_utility.js"/>
Index: binaries/data/mods/public/gui/loading/loading.xml
===================================================================
--- binaries/data/mods/public/gui/loading/loading.xml
+++ binaries/data/mods/public/gui/loading/loading.xml
@@ -7,6 +7,7 @@
 -->
 <objects>
 
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/common/functions_global_object.js"/>
 
 	<script file="gui/loading/loading.js"/>
Index: binaries/data/mods/public/gui/lobby/lobby.js
===================================================================
--- binaries/data/mods/public/gui/lobby/lobby.js
+++ binaries/data/mods/public/gui/lobby/lobby.js
@@ -1040,9 +1040,8 @@
 	sgGameStartTime.hidden = !game.startTime;
 	if (game.startTime)
 		sgGameStartTime.caption = sprintf(
-			// Translation: %(time)s is the hour and minute here.
 			translate("Game started at %(time)s"), {
-				"time": Engine.FormatMillisecondsIntoDateStringLocal(+game.startTime*1000, translate("HH:mm"))
+				"time": timeOfDayToString(+game.startTime * 1000)
 			});
 
 	sgNbPlayers.caption = sprintf(
@@ -1400,19 +1399,9 @@
 	if (Engine.ConfigDB_GetValue("user", "chat.timestamp") != "true")
 		return formattedMessage;
 
-	// Translation: Time as shown in the multiplayer lobby (when you enable it in the options page).
-	// For a list of symbols that you can use, see:
-	// https://sites.google.com/site/icuprojectuserguide/formatparse/datetime?pli=1#TOC-Date-Field-Symbol-Table
-	let timeString = Engine.FormatMillisecondsIntoDateStringLocal(msg.time ? msg.time * 1000 : Date.now(), translate("HH:mm"));
-
-	// Translation: Time prefix as shown in the multiplayer lobby (when you enable it in the options page).
-	let timePrefixString = sprintf(translate("\\[%(time)s]"), {
-		"time": timeString
-	});
-
 	// Translation: IRC message format when there is a time prefix.
 	return sprintf(translate("%(time)s %(message)s"), {
-		"time": senderFont(timePrefixString),
+		"time": senderFont(chatTimestampToString(msg.time ? msg.time * 1000 : Date.now())),
 		"message": formattedMessage
 	});
  }
Index: binaries/data/mods/public/gui/lobby/lobby.xml
===================================================================
--- binaries/data/mods/public/gui/lobby/lobby.xml
+++ binaries/data/mods/public/gui/lobby/lobby.xml
@@ -2,6 +2,7 @@
 
 <objects>
 
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/common/color.js"/>
 	<script file="gui/common/functions_global_object.js"/>
 	<script file="gui/common/functions_utility.js"/>
Index: binaries/data/mods/public/gui/locale/locale.xml
===================================================================
--- binaries/data/mods/public/gui/locale/locale.xml
+++ binaries/data/mods/public/gui/locale/locale.xml
@@ -2,6 +2,7 @@
 
 <objects>
 
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/common/functions_global_object.js"/>
 	<script file="gui/locale/locale.js"/>
 
Index: binaries/data/mods/public/gui/locale/locale_advanced.xml
===================================================================
--- binaries/data/mods/public/gui/locale/locale_advanced.xml
+++ binaries/data/mods/public/gui/locale/locale_advanced.xml
@@ -2,6 +2,7 @@
 
 <objects>
 
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/common/functions_global_object.js"/>
 	<script file="gui/locale/locale_advanced.js"/>
 
Index: binaries/data/mods/public/gui/manual/manual.xml
===================================================================
--- binaries/data/mods/public/gui/manual/manual.xml
+++ binaries/data/mods/public/gui/manual/manual.xml
@@ -1,6 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 
 <objects>
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/common/functions_global_object.js"/>
 	<script file="gui/manual/manual.js"/>
 
Index: binaries/data/mods/public/gui/msgbox/msgbox.xml
===================================================================
--- binaries/data/mods/public/gui/msgbox/msgbox.xml
+++ binaries/data/mods/public/gui/msgbox/msgbox.xml
@@ -1,6 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 
 <objects>
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/msgbox/msgbox.js"/>
 	<script file="gui/common/functions_global_object.js"/>
 
Index: binaries/data/mods/public/gui/options/options.xml
===================================================================
--- binaries/data/mods/public/gui/options/options.xml
+++ binaries/data/mods/public/gui/options/options.xml
@@ -2,6 +2,7 @@
 
 <objects>
 
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/common/functions_global_object.js"/>
 	<script file="gui/options/options.js"/>
 
Index: binaries/data/mods/public/gui/pregame/mainmenu.xml
===================================================================
--- binaries/data/mods/public/gui/pregame/mainmenu.xml
+++ binaries/data/mods/public/gui/pregame/mainmenu.xml
@@ -1,6 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 
 <objects>
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/common/music.js"/>
 	<script file="gui/common/functions_global_object.js"/>
 	<script file="gui/pregame/mainmenu.js"/>
Index: binaries/data/mods/public/gui/prelobby/prelobby.xml
===================================================================
--- binaries/data/mods/public/gui/prelobby/prelobby.xml
+++ binaries/data/mods/public/gui/prelobby/prelobby.xml
@@ -2,6 +2,7 @@
 
 <objects>
 
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/common/functions_global_object.js"/>
 	<script file="gui/common/functions_utility.js"/>
 
Index: binaries/data/mods/public/gui/reference/structree/structree.xml
===================================================================
--- binaries/data/mods/public/gui/reference/structree/structree.xml
+++ binaries/data/mods/public/gui/reference/structree/structree.xml
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <objects>
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/common/functions_civinfo.js"/>
 	<script file="gui/common/functions_global_object.js"/>
 	<script file="gui/common/functions_utility.js"/>
Index: binaries/data/mods/public/gui/replaymenu/replay_menu.js
===================================================================
--- binaries/data/mods/public/gui/replaymenu/replay_menu.js
+++ binaries/data/mods/public/gui/replaymenu/replay_menu.js
@@ -296,7 +296,7 @@
  */
 function getReplayDateTime(replay)
 {
-	return Engine.FormatMillisecondsIntoDateStringLocal(replay.attribs.timestamp * 1000, translate("yyyy-MM-dd HH:mm"));
+	return datetimeToString(replay.attribs.timestamp * 1000);
 }
 
 /**
@@ -320,23 +320,23 @@
 }
 
 /**
- * Returns the month of the given replay in the format "yyyy-MM".
+ * Returns a human-readable version of the month of the given replay.
  *
  * @returns {string}
  */
 function getReplayMonth(replay)
 {
-	return Engine.FormatMillisecondsIntoDateStringLocal(replay.attribs.timestamp * 1000, translate("yyyy-MM"));
+	return monthToString(replay.attribs.timestamp * 1000);
 }
 
 /**
- * Returns a human-readable version of the time when the replay started.
+ * Returns a human-readable version of the duration of the replay.
  *
  * @returns {string}
  */
 function getReplayDuration(replay)
 {
-	return timeToString(replay.duration * 1000);
+	return durationToString(replay.duration * 1000);
 }
 
 /**
Index: binaries/data/mods/public/gui/replaymenu/replay_menu.xml
===================================================================
--- binaries/data/mods/public/gui/replaymenu/replay_menu.xml
+++ binaries/data/mods/public/gui/replaymenu/replay_menu.xml
@@ -2,6 +2,8 @@
 
 <objects>
 
+	<script file="gui/common/l10n.js"/>
+
 	<!-- Used to display game info. -->
 	<script file="gui/common/color.js" />
 	<script file="gui/common/functions_civinfo.js" />
Index: binaries/data/mods/public/gui/savedgames/load.js
===================================================================
--- binaries/data/mods/public/gui/savedgames/load.js
+++ binaries/data/mods/public/gui/savedgames/load.js
@@ -111,7 +111,7 @@
 	setMapPreviewImage("savedInfoPreview", mapData.preview);
 
 	Engine.GetGUIObjectByName("savedPlayers").caption = metadata.initAttributes.settings.PlayerData.length - 1;
-	Engine.GetGUIObjectByName("savedPlayedTime").caption = timeToString(metadata.gui.timeElapsed ? metadata.gui.timeElapsed : 0);
+	Engine.GetGUIObjectByName("savedPlayedTime").caption = durationToString(metadata.gui.timeElapsed ? metadata.gui.timeElapsed : 0);
 	Engine.GetGUIObjectByName("savedMapType").caption = translateMapType(metadata.initAttributes.mapType);
 	Engine.GetGUIObjectByName("savedMapSize").caption = translateMapSize(metadata.initAttributes.settings.Size);
 	Engine.GetGUIObjectByName("savedVictory").caption = translateVictoryCondition(metadata.initAttributes.settings.GameType);
Index: binaries/data/mods/public/gui/savedgames/load.xml
===================================================================
--- binaries/data/mods/public/gui/savedgames/load.xml
+++ binaries/data/mods/public/gui/savedgames/load.xml
@@ -2,6 +2,7 @@
 
 <objects>
 
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/common/color.js" />
 	<script file="gui/common/functions_civinfo.js"/>
 	<script file="gui/common/functions_global_object.js" />
Index: binaries/data/mods/public/gui/savedgames/save.xml
===================================================================
--- binaries/data/mods/public/gui/savedgames/save.xml
+++ binaries/data/mods/public/gui/savedgames/save.xml
@@ -2,6 +2,7 @@
 
 <objects>
 
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/common/color.js"/>
 	<script file="gui/common/functions_global_object.js" />
 	<script file="gui/common/functions_utility_loadsave.js" />
Index: binaries/data/mods/public/gui/session/menu.js
===================================================================
--- binaries/data/mods/public/gui/session/menu.js
+++ binaries/data/mods/public/gui/session/menu.js
@@ -397,7 +397,7 @@
 	let diplomacyCeasefireCounter = Engine.GetGUIObjectByName("diplomacyCeasefireCounter");
 	diplomacyCeasefireCounter.caption = sprintf(
 		translateWithContext("ceasefire", "Time remaining until ceasefire is over: %(time)s."),
-		{ "time": timeToString(simState.ceasefireTimeRemaining) }
+		{ "time": durationToString(simState.ceasefireTimeRemaining) }
 	);
 	diplomacyCeasefireCounter.hidden = !isCeasefireActive;
 }
Index: binaries/data/mods/public/gui/session/messages.js
===================================================================
--- binaries/data/mods/public/gui/session/messages.js
+++ binaries/data/mods/public/gui/session/messages.js
@@ -590,7 +590,7 @@
 		if (n.translateParameters)
 			translateObjectKeys(parameters, n.translateParameters);
 
-		parameters.time = timeToString(n.endTime - GetSimState().timeElapsed);
+		parameters.time = durationToString(n.endTime - g_SimState.timeElapsed);
 
 		colorizePlayernameParameters(parameters);
 
@@ -901,9 +901,7 @@
 	// Save to chat history
 	let historical = {
 		"txt": formatted,
-		"timePrefix": sprintf(translate("\\[%(time)s]"), {
-			"time": Engine.FormatMillisecondsIntoDateStringLocal(Date.now(), translate("HH:mm"))
-		}),
+		"timePrefix": chatTimestampToString(Date.now()),
 		"filter": {}
 	};
 
Index: binaries/data/mods/public/gui/session/selection_panels.js
===================================================================
--- binaries/data/mods/public/gui/session/selection_panels.js
+++ binaries/data/mods/public/gui/session/selection_panels.js
@@ -641,8 +641,7 @@
 
 		// Show the time remaining to finish the first item
 		if (data.i == 0)
-			Engine.GetGUIObjectByName("queueTimeRemaining").caption =
-				Engine.FormatMillisecondsIntoDateStringGMT(queuedItem.timeRemaining, translateWithContext("countdown format", "m:ss"));
+			Engine.GetGUIObjectByName("queueTimeRemaining").caption = durationToString(data.item.timeRemaining);
 
 		let guiObject = Engine.GetGUIObjectByName("unitQueueProgressSlider["+data.i+"]");
 		let size = guiObject.size;
Index: binaries/data/mods/public/gui/session/session.js
===================================================================
--- binaries/data/mods/public/gui/session/session.js
+++ binaries/data/mods/public/gui/session/session.js
@@ -1408,15 +1408,15 @@
 		if (currentSpeed != 1.0)
 			// Translation: The "x" means "times", with the mathematical meaning of multiplication.
 			counters.push(sprintf(translate("%(time)s (%(speed)sx)"), {
-				"time": timeToString(simState.timeElapsed),
+				"time": durationToString(simState.timeElapsed),
 				"speed": Engine.FormatDecimalNumberIntoString(currentSpeed)
 			}));
 		else
-			counters.push(timeToString(simState.timeElapsed));
+			counters.push(durationToString(simState.timeElapsed));
 	}
 
 	if (simState.ceasefireActive && Engine.ConfigDB_GetValue("user", "gui.session.ceasefirecounter") === "true")
-		counters.push(timeToString(simState.ceasefireTimeRemaining));
+		counters.push(durationToString(simState.ceasefireTimeRemaining));
 
 	g_ResearchListTop = 4 + 14 * counters.length;
 }
Index: binaries/data/mods/public/gui/session/session.xml
===================================================================
--- binaries/data/mods/public/gui/session/session.xml
+++ binaries/data/mods/public/gui/session/session.xml
@@ -2,6 +2,7 @@
 
 <objects>
 
+<script file="gui/common/l10n.js"/>
 <script file="gui/common/color.js"/>
 <script file="gui/common/colorFades.js"/>
 <script file="gui/common/functions_civinfo.js"/>
Index: binaries/data/mods/public/gui/splashscreen/splashscreen.xml
===================================================================
--- binaries/data/mods/public/gui/splashscreen/splashscreen.xml
+++ binaries/data/mods/public/gui/splashscreen/splashscreen.xml
@@ -1,6 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 
 <objects>
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/common/functions_global_object.js"/>
 	<script file="gui/splashscreen/splashscreen.js"/>
 
Index: binaries/data/mods/public/gui/summary/summary.js
===================================================================
--- binaries/data/mods/public/gui/summary/summary.js
+++ binaries/data/mods/public/gui/summary/summary.js
@@ -431,7 +431,7 @@
 
 	Engine.GetGUIObjectByName("timeElapsed").caption = sprintf(
 		translate("Game time elapsed: %(time)s"), {
-			"time": timeToString(g_GameData.sim.timeElapsed)
+			"time": durationToString(g_GameData.sim.timeElapsed)
 	});
 
 	let mapType = g_Settings.MapTypes.find(mapType => mapType.Name == g_GameData.sim.mapSettings.mapType);
Index: binaries/data/mods/public/gui/summary/summary.xml
===================================================================
--- binaries/data/mods/public/gui/summary/summary.xml
+++ binaries/data/mods/public/gui/summary/summary.xml
@@ -1,6 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 
 <objects>
+	<script file="gui/common/l10n.js"/>
 	<script file="gui/common/functions_global_object.js"/>
 	<script file="gui/common/functions_civinfo.js"/>
 	<script file="gui/common/functions_utility.js"/>