feat(i18n): enhance internationalization workflow and add catalog checks

Author: PierreRaybaut

.github/copilot-instructions.md

@@ -127,6 +127,17 @@ helpers — prefer the typed path for new work.
 - **Pyodide version is pinned** (`PYODIDE_VERSION` in `runtime.ts` and the
   `<script>` tag in `index.html`). Bump both together; Pyodide’s wheel index
   is version-specific.
+- **Internationalisation is mandatory for user-facing strings**: wrap every
+  new visible string in `t("English source")` (from `src/i18n/translate`;
+  the English text _is_ the key). Use `t("Delete {count}", { count })` for
+  interpolation. Do **not** translate brand names or AI-assistant system
+  prompts. Watch for `t` shadowing in `.map((t) => …)` (rename the param).
+  Literal `t("…")` calls are auto-extracted; keys passed only as a variable
+  (`t(label)`) must be listed in `src/locales/_dynamic-keys.json`. After
+  adding strings, run the **`🌍 i18n: Extract keys (step 1/2)`** task, fill
+  the new empty values in `src/locales/fr.json`, then run the
+  **`🌍 i18n: Check catalog (step 2/2)`** task. See the README
+  "Internationalisation" section for the full workflow.
 
 ## Testing
 
@@ -153,6 +164,9 @@ done (bug fix, feature, or any phase of a multi-phase task):
    a pixel) rather than just calling `window.runtime.*` from
    `page.evaluate`, which can silently no-op.
 3. **For `src/runtime/*.py` changes**, run pytest (`tests/python`).
+4. **When you add or change user-facing strings**, run `npm run i18n:check`
+   (or the `🌍 i18n: Check catalog (step 2/2)` task). CI fails on missing or
+   empty catalog keys.
 
 ## Git workflow
 

.github/workflows/tests.yml

@@ -69,6 +69,9 @@ jobs:
       - name: Lint
         run: npm run lint
 
+      - name: i18n catalog check
+        run: npm run i18n:check
+
       - name: Run Vitest with coverage
         run: npm run test:cov
 

.vscode/tasks.json

@@ -134,6 +134,38 @@
       },
       "problemMatcher": []
     },
+    {
+      "label": "🌍 i18n: Extract keys (step 1/2)",
+      "detail": "Step 1/2 — scan src/ for t(\"…\") calls and merge new keys into src/locales/fr.json (empty placeholders). Then fill the new French values by hand, and run step 2/2 to verify.",
+      "type": "shell",
+      "command": "npm",
+      "args": ["run", "i18n:extract"],
+      "options": {
+        "cwd": "${workspaceFolder}"
+      },
+      "group": "build",
+      "presentation": {
+        "panel": "dedicated",
+        "reveal": "always"
+      },
+      "problemMatcher": []
+    },
+    {
+      "label": "🌍 i18n: Check catalog (step 2/2)",
+      "detail": "Step 2/2 — verify every referenced key is present and non-empty in src/locales/fr.json (read-only; same check as CI). Run after filling in the French translations.",
+      "type": "shell",
+      "command": "npm",
+      "args": ["run", "i18n:check"],
+      "options": {
+        "cwd": "${workspaceFolder}"
+      },
+      "group": "build",
+      "presentation": {
+        "panel": "dedicated",
+        "reveal": "always"
+      },
+      "problemMatcher": []
+    },
     {
       "label": "🚀 Pytest (Python)",
       "type": "shell",