fix(translate): say why Translate did nothing (#287)

When a message was already in the target language, or its language
could not be detected, Translate switched itself back off with no chip,
no "Translating…" and no error. Show a short toast instead: "This
message is already in English." or "Couldn't tell what language this
message is in, so it wasn't translated."

Fixes #287

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/app/hooks/useMessageTranslation.ts

@@ -12,7 +12,8 @@ import {
   markAutoTranslateTried,
 } from '../state/translation';
 import { chromeTranslationEngine as engine } from '../utils/translation/chromeEngine';
-import { sameLanguage } from '../utils/translation/langUtils';
+import { sameLanguage, translateSkipMessage } from '../utils/translation/langUtils';
+import { toastQueueAtom } from '../state/toast';
 
 export type MsgTranslationStatus =
   | 'idle' // not translating (original shown)
@@ -52,6 +53,7 @@ export const useMessageTranslation = (eventId: string, text: string): MsgTransla
   // Write-only: reading the whole cache array here (via useAtom) would
   // resubscribe this message to every other message's writes. [Gitea #39]
   const setCache = useSetAtom(translationCacheAtom);
+  const setToast = useSetAtom(toastQueueAtom);
 
   // The key includes a fingerprint of `text`, so an edit (same event id, new
   // body) misses the old entry and re-translates instead of showing stale
@@ -124,6 +126,16 @@ export const useMessageTranslation = (eventId: string, text: string): MsgTransla
         if (!from || sameLanguage(from, targetLang)) {
           setStatus('skipped');
           setActive(false);
+          // [Gitea #287] Say why nothing happened instead of silently undoing
+          // the click (no chip shows once translation is switched back off).
+          setToast({
+            id: `translate-skipped-${eventId}-${Date.now()}`,
+            displayName: 'Translate',
+            body: translateSkipMessage(from, targetLang),
+            roomName: '',
+            roomId: '',
+            onClick: () => undefined,
+          });
           return;
         }
         setFromLang(from);
@@ -154,7 +166,7 @@ export const useMessageTranslation = (eventId: string, text: string): MsgTransla
       // Invalidate this run's writes if inputs change / unmount.
       runIdRef.current += 1;
     };
-  }, [active, cached, supported, text, targetLang, key, setActive, setCache]);
+  }, [active, cached, supported, text, targetLang, key, setActive, setCache, setToast, eventId]);
 
   // When switched off, drop back to idle (keep the cached translation around so
   // toggling back on is instant).

src/app/utils/translation/langUtils.ts

@@ -85,3 +85,9 @@ export function languageName(code: string, uiLocale = 'en'): string {
 export function isSupportedTargetLang(code: string): boolean {
   return CURATED_NAME.has(normalizeLang(code));
 }
+
+/** Pure: why a manual Translate did nothing (#287). */
+export const translateSkipMessage = (from: string | undefined, targetLang: string): string =>
+  from
+    ? `This message is already in ${languageName(targetLang) || targetLang}.`
+    : "Couldn't tell what language this message is in, so it wasn't translated.";

src/app/utils/translation/translateSkip.test.ts

@@ -0,0 +1,8 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { translateSkipMessage } from './langUtils';
+
+test('translateSkipMessage explains a Translate that did nothing (#287)', () => {
+  assert.equal(translateSkipMessage('en', 'en'), 'This message is already in English.');
+  assert.match(translateSkipMessage(undefined, 'en'), /^Couldn't tell what language/);
+});