diff --git a/lib/widgets/emoji_reaction.dart b/lib/widgets/emoji_reaction.dart
index 3d87b7a8a0a..3107f66f563 100644
--- a/lib/widgets/emoji_reaction.dart
+++ b/lib/widgets/emoji_reaction.dart
@@ -1,5 +1,6 @@
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter_gen/gen_l10n/zulip_localizations.dart';
 
 import '../api/model/model.dart';
 import '../api/route/messages.dart';
@@ -143,6 +144,7 @@ class ReactionChip extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final store = PerAccountStoreWidget.of(context);
+    final zulipLocalizations = ZulipLocalizations.of(context);
 
     final reactionType = reactionWithVotes.reactionType;
     final emojiCode = reactionWithVotes.emojiCode;
@@ -157,7 +159,7 @@ class ReactionChip extends StatelessWidget {
       ? userIds.map((id) {
           return id == store.selfUserId
             ? 'You'
-            : store.users[id]?.fullName ?? '(unknown user)'; // TODO(i18n)
+            : store.users[id]?.fullName ?? zulipLocalizations.unknownUserName;
         }).join(', ')
       : userIds.length.toString();
 
diff --git a/lib/widgets/inbox.dart b/lib/widgets/inbox.dart
index 9259c813649..c94a0ae8fdb 100644
--- a/lib/widgets/inbox.dart
+++ b/lib/widgets/inbox.dart
@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:flutter_gen/gen_l10n/zulip_localizations.dart';
 
 import '../api/model/model.dart';
 import '../model/narrow.dart';
@@ -368,18 +369,21 @@ class _DmItem extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final store = PerAccountStoreWidget.of(context);
+    final zulipLocalizations = ZulipLocalizations.of(context);
     final selfUser = store.users[store.selfUserId]!;
 
     final designVariables = DesignVariables.of(context);
 
     final title = switch (narrow.otherRecipientIds) { // TODO dedupe with [RecentDmConversationsItem]
       [] => selfUser.fullName,
-      [var otherUserId] => store.users[otherUserId]?.fullName ?? '(unknown user)',
+      [var otherUserId] => store.users[otherUserId]?.fullName ?? zulipLocalizations.unknownUserName,
 
       // TODO(i18n): List formatting, like you can do in JavaScript:
       //   new Intl.ListFormat('ja').format(['Chris', 'Greg', 'Alya', 'Shu'])
       //   // 'Chris、Greg、Alya、Shu'
-      _ => narrow.otherRecipientIds.map((id) => store.users[id]?.fullName ?? '(unknown user)').join(', '),
+      _ => narrow.otherRecipientIds.map((id) =>
+              store.users[id]?.fullName ?? zulipLocalizations.unknownUserName
+           ).join(', '),
     };
 
     return Material(
diff --git a/lib/widgets/message_list.dart b/lib/widgets/message_list.dart
index 29bd244fdb0..01e8057143c 100644
--- a/lib/widgets/message_list.dart
+++ b/lib/widgets/message_list.dart
@@ -335,12 +335,15 @@ class MessageListAppBarTitle extends StatelessWidget {
       case ChannelNarrow(:var streamId):
         final store = PerAccountStoreWidget.of(context);
         final stream = store.streams[streamId];
+        // TODO(i18n): provide translations just as
+        //  'zulipLocalizations.unknownUserName' for 'unknown channel'
         final streamName = stream?.name ?? '(unknown channel)';
         return _buildStreamRow(context, stream: stream, text: streamName);
 
       case TopicNarrow(:var streamId, :var topic):
         final store = PerAccountStoreWidget.of(context);
         final stream = store.streams[streamId];
+        // TODO(i18n): provide translations for 'unknown channel'
         final streamName = stream?.name ?? '(unknown channel)';
         return _buildStreamRow(context, stream: stream, text: "$streamName > $topic");
 
@@ -349,7 +352,8 @@ class MessageListAppBarTitle extends StatelessWidget {
         if (otherRecipientIds.isEmpty) {
           return const Text("DMs with yourself");
         } else {
-          final names = otherRecipientIds.map((id) => store.users[id]?.fullName ?? '(unknown user)');
+          final names = otherRecipientIds.map((id) =>
+            store.users[id]?.fullName ?? zulipLocalizations.unknownUserName);
           return Text("DMs with ${names.join(", ")}"); // TODO show avatars
         }
     }
diff --git a/lib/widgets/profile.dart b/lib/widgets/profile.dart
index 90f2512042c..fe5a367a470 100644
--- a/lib/widgets/profile.dart
+++ b/lib/widgets/profile.dart
@@ -290,8 +290,9 @@ class _UserWidget extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final store = PerAccountStoreWidget.of(context);
+    final zulipLocalizations = ZulipLocalizations.of(context);
     final user = store.users[userId];
-    final fullName = user?.fullName ?? '(unknown user)';
+    final fullName = user?.fullName ?? zulipLocalizations.unknownUserName;
     return InkWell(
       onTap: () => Navigator.push(context,
         ProfilePage.buildRoute(context: context,
diff --git a/lib/widgets/recent_dm_conversations.dart b/lib/widgets/recent_dm_conversations.dart
index b8d72e192e2..78be5bff954 100644
--- a/lib/widgets/recent_dm_conversations.dart
+++ b/lib/widgets/recent_dm_conversations.dart
@@ -93,6 +93,7 @@ class RecentDmConversationsItem extends StatelessWidget {
   Widget build(BuildContext context) {
     final store = PerAccountStoreWidget.of(context);
     final selfUser = store.users[store.selfUserId]!;
+    final zulipLocalizations = ZulipLocalizations.of(context);
 
     final designVariables = DesignVariables.of(context);
 
@@ -107,13 +108,15 @@ class RecentDmConversationsItem extends StatelessWidget {
         //   (should we offer a "spam folder" style summary screen of recent
         //   1:1 DM conversations from muted users?)
         final otherUser = store.users[otherUserId];
-        title = otherUser?.fullName ?? '(unknown user)';
+        title = otherUser?.fullName ?? zulipLocalizations.unknownUserName;
         avatar = AvatarImage(userId: otherUserId, size: _avatarSize);
       default:
         // TODO(i18n): List formatting, like you can do in JavaScript:
         //   new Intl.ListFormat('ja').format(['Chris', 'Greg', 'Alya'])
         //   // 'Chris、Greg、Alya'
-        title = narrow.otherRecipientIds.map((id) => store.users[id]?.fullName ?? '(unknown user)').join(', ');
+        title = narrow.otherRecipientIds.map((id) =>
+            store.users[id]?.fullName ?? zulipLocalizations.unknownUserName
+          ).join(', ');
         avatar = ColoredBox(color: designVariables.groupDmConversationIconBg,
           child: Center(
             child: Icon(color: designVariables.groupDmConversationIcon,