feat: dedupe bilingual() identical sides + add CTA ja/zh translations

docs/CHANGELOG.md

@@ -59,6 +59,21 @@ This PR adds a proper Spanish branch in both blocks:
 French CBT scaffolding stays as the explicit default fallback. No behavior change for any other language.
 
 **Why:** Spanish was target-language #2 added to the app, but the original French edge function was never split. The bug only surfaced when the language-* consolidation reorganized the file. Catching it now keeps the granularity goal honest — coaching prompts should be in the target language, full stop.
+---
+### Bilingual rendering — dedupe identical sides, CTA gets Japanese + Chinese
+
+**Fixes the "Write today / Write today" rendering when the active pair has no translation for either side.**
+
+Two changes:
+
+1. **`bilingual()` dedupes identical sides.** When `targetLang` and `primaryLang` resolve to the same string (typically because both fell back to English via the Translations fallback chain), the helper now returns the string once instead of `"X / X"`. Silent improvement for every call site across the app — no API change, no semantic change for pairs that legitimately differ (e.g. `fr / en`).
+
+2. **HomeScreen CTA gets explicit Japanese, Simplified Chinese, and Traditional Chinese keys.** "Write today" / "Write another" now render correctly when the target is `ja` or the primary is `zh-Hans` / `zh-Hant`:
+   - ja: `今日書きましょう` / `もう一度書きましょう` (polite, inviting register)
+   - zh-Hans: `今天写日记` / `再写一篇`
+   - zh-Hant: `今天寫日記` / `再寫一篇`
+
+**Why partial:** the CTA is the most visually prominent bilingual call on Home, so it gets translations now. The rest of the chrome (`Brain Dump`, `Thought Garden`, `French journaling practice`, `More tools`, etc.) is silently improved by the dedupe alone — they no longer say `"Brain Dump / Brain Dump"` when both sides fall back. A future translation-pass PR will add `ja:` and `zh-*:` keys to the remaining anchors.
 
 ### Japanese language support — target-only
 

src/components/journal/HomeScreen.tsx

@@ -167,8 +167,22 @@ export function HomeScreen({ hasJournaledToday, streak, totalDays, totalWords, e
           >
             <Feather className="w-5 h-5 mr-2" />
             {hasJournaledToday
-              ? bilingual({ fr: 'Écrire encore', en: 'Write another', es: 'Escribir más' })
-              : bilingual({ fr: "Écrire aujourd'hui", en: 'Write today', es: 'Escribir hoy' })
+              ? bilingual({
+                  fr: 'Écrire encore',
+                  en: 'Write another',
+                  es: 'Escribir más',
+                  ja: 'もう一度書きましょう',
+                  'zh-Hans': '再写一篇',
+                  'zh-Hant': '再寫一篇',
+                })
+              : bilingual({
+                  fr: "Écrire aujourd'hui",
+                  en: 'Write today',
+                  es: 'Escribir hoy',
+                  ja: '今日書きましょう',
+                  'zh-Hans': '今天写日记',
+                  'zh-Hant': '今天寫日記',
+                })
             }
           </Button>
 

src/contexts/LanguageContext.test.tsx

@@ -263,6 +263,37 @@ describe('bilingual() — formatted pair', () => {
     expect(result.current.bilingual({ fr: 'Vide-tête', en: 'Brain Dump', es: 'Volcado mental' }))
       .toBe('Vide-tête / Brain Dump');
   });
+
+  it('dedupes when target and primary resolve to the same string', () => {
+    // target=ja primary=zh-Hant; neither key present → both fall back to en.
+    // bilingual() should render once, not "Write today / Write today".
+    localStorage.setItem(STORAGE_KEY, JSON.stringify({ primary: 'zh-Hant', target: 'ja' }));
+    const { result } = renderHook(() => useLanguage(), { wrapper });
+    expect(result.current.bilingual({ fr: "Écrire aujourd'hui", en: 'Write today', es: 'Escribir hoy' }))
+      .toBe('Write today');
+  });
+
+  it('does not dedupe when target and primary differ', () => {
+    // target=fr primary=en — both resolve and differ → keep the pair.
+    const { result } = renderHook(() => useLanguage(), { wrapper });
+    expect(result.current.bilingual({ fr: "Écrire aujourd'hui", en: 'Write today', es: 'Escribir hoy' }))
+      .toBe("Écrire aujourd'hui / Write today");
+  });
+
+  it('renders both when ja and zh-Hant keys are provided', () => {
+    // Same pair as the dedupe case, but now both keys are present → no fallback,
+    // no dedupe, both strings render.
+    localStorage.setItem(STORAGE_KEY, JSON.stringify({ primary: 'zh-Hant', target: 'ja' }));
+    const { result } = renderHook(() => useLanguage(), { wrapper });
+    expect(result.current.bilingual({
+      fr: "Écrire aujourd'hui",
+      en: 'Write today',
+      es: 'Escribir hoy',
+      ja: '今日書きましょう',
+      'zh-Hans': '今天写日记',
+      'zh-Hant': '今天寫日記',
+    })).toBe('今日書きましょう / 今天寫日記');
+  });
 });
 
 describe('stringFor() — dev-mode fallback warning', () => {

src/contexts/LanguageContext.tsx

@@ -165,7 +165,9 @@ export function LanguageProvider({ children }: { children: ReactNode }) {
   const bilingual = (translations: Translations) => {
     const tgt = stringFor(pair.target, translations);
     const prm = stringFor(pair.primary, translations);
-    return `${tgt} / ${prm}`;
+    // Dedupe: when target and primary resolve to the same string (typically
+    // because both fell back to en), render once instead of "X / X".
+    return tgt === prm ? tgt : `${tgt} / ${prm}`;
   };
 
   return (