diff --git a/apps/server/src/terminal/Manager.test.ts b/apps/server/src/terminal/Manager.test.ts
index 1cf7e8dffec..8fa7bbf019e 100644
--- a/apps/server/src/terminal/Manager.test.ts
+++ b/apps/server/src/terminal/Manager.test.ts
@@ -1391,6 +1391,36 @@ it.layer(
     }),
   );
 
+  it.effect("falls back to a UTF-8 LANG when the host env has no locale", () =>
+    Effect.gen(function* () {
+      const { manager, ptyAdapter } = yield* createManager(5, {
+        env: { PATH: "/usr/bin:/bin" },
+      }).pipe(Effect.provide(withHostPlatform("darwin")));
+      yield* manager.open(openInput());
+      const spawnInput = ptyAdapter.spawnInputs[0];
+      expect(spawnInput).toBeDefined();
+      if (!spawnInput) return;
+
+      // Without this fallback a Dock-launched app spawns the PTY in the C
+      // locale and zsh mangles multibyte input into `?`/`<00xx>` bytes.
+      expect(spawnInput.env.LANG).toBe("en_US.UTF-8");
+    }),
+  );
+
+  it.effect("keeps an explicitly configured locale untouched", () =>
+    Effect.gen(function* () {
+      const { manager, ptyAdapter } = yield* createManager(5, {
+        env: { PATH: "/usr/bin:/bin", LANG: "ru_RU.KOI8-R" },
+      }).pipe(Effect.provide(withHostPlatform("darwin")));
+      yield* manager.open(openInput());
+      const spawnInput = ptyAdapter.spawnInputs[0];
+      expect(spawnInput).toBeDefined();
+      if (!spawnInput) return;
+
+      expect(spawnInput.env.LANG).toBe("ru_RU.KOI8-R");
+    }),
+  );
+
   it.effect("injects runtime env overrides into spawned terminals", () =>
     Effect.gen(function* () {
       const { manager, ptyAdapter } = yield* createManager();
diff --git a/apps/server/src/terminal/Manager.ts b/apps/server/src/terminal/Manager.ts
index caa5106bb9f..a260e891be3 100644
--- a/apps/server/src/terminal/Manager.ts
+++ b/apps/server/src/terminal/Manager.ts
@@ -1112,9 +1112,24 @@ function stripAppImageRuntimeEnv(env: NodeJS.ProcessEnv): NodeJS.ProcessEnv {
   return scrubbed;
 }
 
+// launchd starts GUI apps without LANG/LC_* (Terminal.app injects its own), so
+// a packaged app's PTY shell lands in the single-byte C locale and zsh's line
+// editor renders multibyte input as raw `?`/`<00xx>` bytes. An explicit LANG or
+// LC_ALL — even a non-UTF-8 one — is the user's choice and is left alone.
+function withUtf8LocaleFallback(
+  env: NodeJS.ProcessEnv,
+  platform: NodeJS.Platform,
+): NodeJS.ProcessEnv {
+  if (platform === "win32") return env;
+  if (env.LC_ALL || env.LANG) return env;
+  // en_US.UTF-8 always exists on macOS; on Linux only C.UTF-8 is guaranteed.
+  return { ...env, LANG: platform === "darwin" ? "en_US.UTF-8" : "C.UTF-8" };
+}
+
 function createTerminalSpawnEnv(
   baseEnv: NodeJS.ProcessEnv,
-  runtimeEnv?: Record<string, string> | null,
+  runtimeEnv: Record<string, string> | undefined | null,
+  platform: NodeJS.Platform,
 ): NodeJS.ProcessEnv {
   const spawnEnv: NodeJS.ProcessEnv = {};
   for (const [key, value] of Object.entries(baseEnv)) {
@@ -1127,7 +1142,7 @@ function createTerminalSpawnEnv(
       spawnEnv[key] = value;
     }
   }
-  return stripAppImageRuntimeEnv(spawnEnv);
+  return withUtf8LocaleFallback(stripAppImageRuntimeEnv(spawnEnv), platform);
 }
 
 function normalizedRuntimeEnv(
@@ -1884,7 +1899,7 @@ export const makeWithOptions = Effect.fn("TerminalManager.makeWithOptions")(func
         Effect.andThen(
           Effect.gen(function* () {
             const shellCandidates = resolveShellCandidates(shellResolver, platform, baseEnv);
-            const terminalEnv = createTerminalSpawnEnv(baseEnv, session.runtimeEnv);
+            const terminalEnv = createTerminalSpawnEnv(baseEnv, session.runtimeEnv, platform);
             const spawnResult = yield* trySpawn(shellCandidates, terminalEnv, session);
             ptyProcess = spawnResult.process;
             startedShell = spawnResult.shellLabel;