ZytriuNks · Sep 14, 2026
diff --git a/apps/web/src/AppRoot.tsx b/apps/web/src/AppRoot.tsx
@@ -4,6 +4,7 @@ import { ElectronBrowserHost } from "./browser/ElectronBrowserHost";
 import { PreviewAutomationHosts } from "./components/preview/PreviewAutomationHosts";
 import { QuitHoldOverlay } from "./components/QuitHoldOverlay";
 import { AppAtomRegistryProvider } from "./rpc/atomRegistry";
+import { I18nProvider } from "./i18n/I18nProvider";
 import type { AppRouter } from "./router";
 
 /**
@@ -13,11 +14,13 @@ import type { AppRouter } from "./router";
  */
 export function AppRoot({ router }: { readonly router: AppRouter }) {
   return (
-    <AppAtomRegistryProvider>
-      <RouterProvider router={router} />
-      <PreviewAutomationHosts />
-      <ElectronBrowserHost />
-      <QuitHoldOverlay />
-    </AppAtomRegistryProvider>
+    <I18nProvider>
+      <AppAtomRegistryProvider>
+        <RouterProvider router={router} />
+        <PreviewAutomationHosts />
+        <ElectronBrowserHost />
+        <QuitHoldOverlay />
+      </AppAtomRegistryProvider>
+    </I18nProvider>
   );
 }
diff --git a/apps/web/src/clientPersistenceStorage.test.ts b/apps/web/src/clientPersistenceStorage.test.ts
@@ -114,6 +114,18 @@ describe("clientPersistenceStorage", () => {
     expect(settings).not.toHaveProperty("diffWordWrap");
   });
 
+  it("keeps the language across reloads and defaults it to the system", async () => {
+    const testWindow = getTestWindow();
+    const { readBrowserClientSettings, writeBrowserClientSettings } =
+      await import("./clientPersistenceStorage");
+
+    testWindow.localStorage.setItem("t3code:client-settings:v1", JSON.stringify({}));
+    expect(readBrowserClientSettings()?.language).toBe("system");
+
+    writeBrowserClientSettings({ ...DEFAULT_CLIENT_SETTINGS, language: "zh-CN" });
+    expect(readBrowserClientSettings()?.language).toBe("zh-CN");
+  });
+
   it("keeps the default diff file state across reloads and defaults it to expanded", async () => {
     const testWindow = getTestWindow();
     const { readBrowserClientSettings, writeBrowserClientSettings } =

diff --git a/apps/web/src/components/CommandPalette.tsx b/apps/web/src/components/CommandPalette.tsx
@@ -74,6 +74,7 @@ import { useHandleNewThread } from "../hooks/useHandleNewThread";
 import { useOpenPanelPullRequestUrl } from "../hooks/useOpenPanelPullRequestUrl";
 import { writeTextToClipboard } from "../hooks/useCopyToClipboard";
 import { useClientSettings } from "../hooks/useSettings";
+import { useConnectionStatusCopy } from "../i18n/I18nProvider";
 import { useTheme } from "../hooks/useTheme";
 import { readLocalApi } from "../localApi";
 import { desktopLocalBackendId } from "../connection/desktopLocal";
@@ -619,6 +620,7 @@ function OpenCommandPaletteDialog(props: {
   readonly openOverlayMode: (mode: SearchOverlayMode) => void;
   readonly clearOpenIntent: () => void;
 }) {
+  const connectionStatusCopy = useConnectionStatusCopy();
   const navigate = useNavigate();
   const pathname = useLocation({ select: (location) => location.pathname });
   const { clearOpenIntent, openIntent, openOverlayMode, setOpen } = props;
@@ -874,7 +876,7 @@ function OpenCommandPaletteDialog(props: {
         isPrimary,
         machine: resolveEnvironmentMachineKind(environment.serverConfig),
         isConnected: canCreateProjectInEnvironment(environment.connection.phase),
-        status: connectionStatusText(environment.connection),
+        status: connectionStatusText(environment.connection, connectionStatusCopy),
       };
     });
 
@@ -886,7 +888,7 @@ function OpenCommandPaletteDialog(props: {
     });
 
     return options;
-  }, [environments]);
+  }, [connectionStatusCopy, environments]);
   const defaultAddProjectEnvironmentId =
     addProjectEnvironmentOptions.find((option) => option.isConnected)?.environmentId ?? null;
   const wslAddProjectEnvironmentOption = useMemo(

diff --git a/apps/web/src/components/DiffPanel.tsx b/apps/web/src/components/DiffPanel.tsx
@@ -49,6 +49,7 @@ import { useWorkspaceMutationRefresh } from "../hooks/useWorkspaceMutationRefres
 import { useProject, useThread } from "../state/entities";
 import { resolveThreadRouteRef } from "../threadRoutes";
 import { useClientSettings, useUpdateClientSettings } from "../hooks/useSettings";
+import { useI18n } from "../i18n/I18nProvider";
 import { formatShortTimestamp } from "../timestampFormat";
 import { DiffFilePathCopyButton } from "./DiffFilePathCopyButton";
 import { DiffPanelLoadingState, DiffPanelShell, type DiffPanelMode } from "./DiffPanelShell";
@@ -110,6 +111,7 @@ export default function DiffPanel({
   initialGitScope: initialGitScopeProp,
   workspaceMutationId,
 }: DiffPanelProps) {
+  const { language, t } = useI18n();
   const { resolvedTheme } = useTheme();
   const settings = useClientSettings();
   const [initialGitScope] = useState(initialGitScopeProp);
@@ -216,21 +218,21 @@ export default function DiffPanel({
   const selectedScopeLabel =
     selectedTurnId === null
       ? selectedGitScope === "unstaged"
-        ? "Working tree"
-        : "Branch changes"
+        ? t("diff.scope.workingTree")
+        : t("diff.scope.branchChanges")
       : selectedTurn?.turnId === latestTurn?.turnId
-        ? "Latest turn"
-        : `Turn ${selectedCheckpointTurnCount ?? "?"}`;
+        ? t("diff.scope.latestTurn")
+        : t("diff.scope.turn", { count: selectedCheckpointTurnCount ?? "?" });
   const reviewSectionId = selectedTurn ? `turn:${selectedTurn.turnId}` : selectedGitScope;
   const collapseScopeKey = routeThreadRef
     ? `${routeThreadRef.environmentId}:${routeThreadRef.threadId}:${reviewSectionId}`
     : null;
   const codeViewMountKey = `${collapseScopeKey ?? reviewSectionId}:${codeViewRevision}`;
   const reviewSectionTitle = selectedTurn
-    ? `Turn ${selectedCheckpointTurnCount ?? "?"}`
+    ? t("diff.scope.turn", { count: selectedCheckpointTurnCount ?? "?" })
     : selectedGitScope === "unstaged"
-      ? "Working tree"
-      : "Branch changes";
+      ? t("diff.scope.workingTree")
+      : t("diff.scope.branchChanges");
   const selectedCheckpointRange = useMemo(
     () =>
       typeof selectedCheckpointTurnCount === "number"
@@ -558,7 +560,7 @@ export default function DiffPanel({
         <DropdownMenu>
           <DropdownMenuTrigger
             className="inline-flex h-6 max-w-full items-center gap-1 rounded-md bg-accent px-2 text-xs font-medium text-accent-foreground outline-none transition-colors hover:bg-accent/80 focus-visible:ring-2 focus-visible:ring-ring"
-            aria-label={`Diff scope: ${selectedScopeLabel}`}
+            aria-label={t("diff.scope.label", { scope: selectedScopeLabel })}
           >
             <span className="truncate">{selectedScopeLabel}</span>
             <ChevronDownIcon className="size-3.5 shrink-0 opacity-70" />
@@ -572,7 +574,7 @@ export default function DiffPanel({
               }
               onClick={() => selectGitScope("unstaged")}
             >
-              <span>Working tree</span>
+              <span>{t("diff.scope.workingTree")}</span>
             </DropdownMenuItem>
             <DropdownMenuItem
               className={
@@ -582,7 +584,7 @@ export default function DiffPanel({
               }
               onClick={() => selectGitScope("branch")}
             >
-              <span>Branch changes</span>
+              <span>{t("diff.scope.branchChanges")}</span>
             </DropdownMenuItem>
             <DropdownMenuItem
               className={
@@ -594,10 +596,10 @@ export default function DiffPanel({
                 if (latestTurn) selectTurn(latestTurn.turnId);
               }}
             >
-              <span>Latest turn</span>
+              <span>{t("diff.scope.latestTurn")}</span>
             </DropdownMenuItem>
             <DropdownMenuSub>
-              <DropdownMenuSubTrigger>Turn</DropdownMenuSubTrigger>
+              <DropdownMenuSubTrigger>{t("diff.scope.turns")}</DropdownMenuSubTrigger>
               <DropdownMenuSubContent className="w-64">
                 {orderedTurnDiffSummaries.map((summary) => {
                   const turnCount =
@@ -612,9 +614,13 @@ export default function DiffPanel({
                       }
                       onClick={() => selectTurn(summary.turnId)}
                     >
-                      <span>Turn {turnCount}</span>
+                      <span>{t("diff.scope.turn", { count: turnCount })}</span>
                       <span className="ml-auto text-xs tabular-nums text-muted-foreground">
-                        {formatShortTimestamp(summary.completedAt, settings.timestampFormat)}
+                        {formatShortTimestamp(
+                          summary.completedAt,
+                          settings.timestampFormat,
+                          language,
+                        )}
                       </span>
                     </DropdownMenuItem>
                   );
@@ -895,15 +901,15 @@ export default function DiffPanel({
     <DiffPanelShell mode={mode} header={headerRow}>
       {!activeThread ? (
         <div className="flex flex-1 items-center justify-center px-5 text-center text-xs text-muted-foreground/70">
-          Select a thread to inspect turn diffs.
+          {t("diff.empty.selectThread")}
         </div>
       ) : !isGitRepo ? (
         <div className="flex flex-1 items-center justify-center px-5 text-center text-xs text-muted-foreground/70">
-          Turn diffs are unavailable because this project is not a git repository.
+          {t("diff.empty.notRepository")}
         </div>
       ) : selectedTurnId !== null && orderedTurnDiffSummaries.length === 0 ? (
         <div className="flex flex-1 items-center justify-center px-5 text-center text-xs text-muted-foreground/70">
-          No completed turns yet.
+          {t("diff.empty.noCompletedTurns")}
         </div>
       ) : (
         <>
@@ -932,11 +938,7 @@ export default function DiffPanel({
                 />
               ) : (
                 <div className="flex h-full items-center justify-center px-3 py-2 text-xs text-muted-foreground/70">
-                  <p>
-                    {hasNoNetChanges
-                      ? "No net changes in this selection."
-                      : "No patch available for this selection."}
-                  </p>
+                  <p>{hasNoNetChanges ? t("diff.empty.noNetChanges") : t("diff.empty.noPatch")}</p>
                 </div>
               )
             ) : renderablePatch.kind === "files" ? (

diff --git a/apps/web/src/components/chat/ChatComposer.tsx b/apps/web/src/components/chat/ChatComposer.tsx
@@ -75,6 +75,7 @@ import {
   replaceTextRange,
 } from "../../composer-logic";
 import { DISCONNECTED_COMPOSER_PLACEHOLDER } from "../../composerPlaceholder";
+import { useI18n } from "../../i18n/I18nProvider";
 import {
   deriveComposerSendState,
   getAntigravitySendBlockReason,
@@ -1430,6 +1431,7 @@ export interface ChatComposerProps {
 // --------------------------------------------------------------------------
 
 export const ChatComposer = memo(function ChatComposer(props: ChatComposerProps) {
+  const { t } = useI18n();
   const {
     composerDraftTarget,
     environmentId,
@@ -6672,12 +6674,12 @@ export const ChatComposer = memo(function ChatComposer(props: ChatComposerProps)
                           : showPlanFollowUpPrompt && activeProposedPlan
                             ? "Add feedback to refine the plan, or leave this blank to implement it"
                             : projectSelectionRequired
-                              ? "Choose a project above to start a thread"
+                              ? t("composer.placeholder.chooseProject")
                               : showProviderUnavailable
-                                ? "Enable a provider in Settings to send a message"
+                                ? t("composer.placeholder.enableProvider")
                                 : phase === "disconnected"
                                   ? DISCONNECTED_COMPOSER_PLACEHOLDER
-                                  : "Ask anything, @tag files/folders, $use skills, or / for commands"
+                                  : t("composer.placeholder.default")
                     }
                     disabled={
                       isConnecting ||

diff --git a/apps/web/src/components/chat/ComposerPrimaryActions.tsx b/apps/web/src/components/chat/ComposerPrimaryActions.tsx
@@ -7,6 +7,7 @@ import { Button } from "../ui/button";
 import { Menu, MenuItem, MenuPopup, MenuTrigger } from "../ui/menu";
 import { Spinner } from "../ui/spinner";
 import { composerFloatingLayerProps } from "./composerEventScope";
+import { useI18n } from "../../i18n/I18nProvider";
 
 interface PendingActionState {
   questionIndex: number;
@@ -81,6 +82,7 @@ export const ComposerPrimaryActions = memo(function ComposerPrimaryActions({
     ? { onPointerDown: preventPointerFocus }
     : undefined;
   const environmentIdentificationMode = useEnvironmentIdentificationMode();
+  const { t } = useI18n();
   const isSendDisabled = sendDisabledReason !== null;
   const stageBackdropVariant = useSidebarStageBackdropVariant(
     environmentIdentificationMode === "artwork",
@@ -99,7 +101,7 @@ export const ComposerPrimaryActions = memo(function ComposerPrimaryActions({
       )}
       {...pointerFocusProps}
       onClick={onInterrupt}
-      aria-label="Stop generation"
+      aria-label={t("composer.stopGeneration")}
     >
       <svg width="12" height="12" viewBox="0 0 12 12" fill="currentColor" aria-hidden="true">
         <rect x="2" y="2" width="8" height="8" rx="1.5" />
@@ -238,16 +240,16 @@ export const ComposerPrimaryActions = memo(function ComposerPrimaryActions({
       }
       aria-label={
         isEnvironmentUnavailable
-          ? "Environment disconnected"
+          ? t("composer.environmentDisconnected")
           : sendDisabledReason
             ? sendDisabledReason
             : isConnecting
-              ? "Connecting"
+              ? t("composer.connecting")
               : isPreparingWorktree
-                ? "Preparing worktree"
+                ? t("composer.preparingWorktree")
                 : isSendBusy
-                  ? "Sending"
-                  : "Send message"
+                  ? t("composer.sending")
+                  : t("composer.sendMessage")
       }
     >
       {stageBackdropVariant ? (

diff --git a/apps/web/src/components/chat/MessagesTimeline.tsx b/apps/web/src/components/chat/MessagesTimeline.tsx
@@ -234,6 +234,8 @@ import { cn } from "~/lib/utils";
 import { useUiStateStore } from "~/uiStateStore";
 import { type TimestampFormat } from "@t3tools/contracts/settings";
 import { formatChatTimestampTooltip, formatDayAwareTimestamp } from "../../timestampFormat";
+import type { AppLanguage } from "../../i18n/locale";
+import { useI18n } from "../../i18n/I18nProvider";
 
 import { SkillInlineText } from "./SkillInlineText";
 import { deriveAgentSpawnSummary } from "./agentSpawnSummary";
@@ -255,6 +257,7 @@ interface TimelineRowSharedState {
   citationRequest: AssistantCitationTarget | null;
   listRef: React.RefObject<LegendListRef | null>;
   timestampFormat: TimestampFormat;
+  language: AppLanguage;
   routeThreadKey: string;
   threadRef: ScopedThreadRef | null;
   markdownCwd: string | undefined;
@@ -485,6 +488,7 @@ export const MessagesTimeline = memo(function MessagesTimeline({
   topFadeEnabled = false,
   loadEarlier = null,
 }: MessagesTimelineProps) {
+  const { language } = useI18n();
   const [expandedTurnIds, setExpandedTurnIds] = useState<ReadonlySet<TurnId>>(new Set());
   const [expandedWorkGroupIds, setExpandedWorkGroupIds] = useState<ReadonlySet<string>>(new Set());
   // Preserve member disclosure state across virtualization.
@@ -898,6 +902,7 @@ export const MessagesTimeline = memo(function MessagesTimeline({
       citationRequest: readyCitationRequest,
       listRef,
       timestampFormat,
+      language,
       routeThreadKey,
       // Keep Markdown callbacks memoized during unrelated activity updates.
       threadRef: citationThreadRef,
@@ -929,6 +934,7 @@ export const MessagesTimeline = memo(function MessagesTimeline({
       readyCitationRequest,
       listRef,
       timestampFormat,
+      language,
       routeThreadKey,
       citationThreadRef,
       markdownCwd,
@@ -1816,10 +1822,15 @@ function UserTimelineRow({ row }: { row: Extract<TimelineRow, { kind: "message"
         <div className="flex shrink-0 items-center gap-2">
           <Tooltip>
             <TooltipTrigger render={<p className="text-muted-foreground text-xs tabular-nums" />}>
-              {formatDayAwareTimestamp(row.message.createdAt, ctx.timestampFormat)}
+              {formatDayAwareTimestamp(
+                row.message.createdAt,
+                ctx.timestampFormat,
+                undefined,
+                ctx.language,
+              )}
             </TooltipTrigger>
             <TooltipPopup>
-              {formatChatTimestampTooltip(row.message.createdAt, ctx.timestampFormat)}
+              {formatChatTimestampTooltip(row.message.createdAt, ctx.timestampFormat, ctx.language)}
             </TooltipPopup>
           </Tooltip>
           <div className="flex items-center gap-0.5">
@@ -2022,10 +2033,15 @@ function AssistantMessageMeta({
       {!message.streaming && (
         <Tooltip>
           <TooltipTrigger render={<p className="text-muted-foreground text-xs tabular-nums" />}>
-            {formatDayAwareTimestamp(message.updatedAt, ctx.timestampFormat)}
+            {formatDayAwareTimestamp(
+              message.updatedAt,
+              ctx.timestampFormat,
+              undefined,
+              ctx.language,
+            )}
           </TooltipTrigger>
           <TooltipPopup>
-            {formatChatTimestampTooltip(message.updatedAt, ctx.timestampFormat)}
+            {formatChatTimestampTooltip(message.updatedAt, ctx.timestampFormat, ctx.language)}
           </TooltipPopup>
         </Tooltip>
       )}