ci: fail when compiled locale modules drift from the Weblate catalogs (#1662)

.github/workflows/tests.yaml

@@ -216,6 +216,48 @@ jobs:
           cargo run --locked --quiet --manifest-path tools/ci/Cargo.toml -- ci
           --step knip
 
+  i18n:
+    runs-on: ubuntu-24.04
+    timeout-minutes: 25
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0
+
+      - name: Set up Rust toolchain (CI helpers)
+        uses: dtolnay/rust-toolchain@e97e2d8cc328f1b50210efc529dca0028893a2d9
+        with:
+          toolchain: "1.93.0"
+          targets: wasm32-unknown-unknown
+
+      - name: Install pnpm
+        uses: pnpm/action-setup@0ebf47130e4866e96fce0953f49152a61190b271
+
+      - name: Install Node.js
+        uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e
+        with:
+          node-version: '24'
+          cache: 'pnpm'
+
+      - name: Install dependencies
+        run: >-
+          cargo run --locked --quiet --manifest-path tools/ci/Cargo.toml -- ci
+          --step install_dependencies
+
+      - name: Compile locale catalogs
+        run: pnpm i18n:compile
+
+      - name: Check drift of compiled locale modules
+        run: |
+          if ! git diff --exit-code -- \
+            packages/errors/src/i18n/locales \
+            packages/errors/src/i18n/ErrorI18nTypes.generated.ts \
+            fluxer_api/pkgs/email/src/email_i18n/locales \
+            fluxer_api/pkgs/email/src/email_i18n/EmailI18nTypes.generated.ts \
+            fluxer_api/src/api/content_i18n/locales; then
+            echo "::error::Compiled locale modules are outdated. Run 'pnpm i18n:compile' and commit the result. Translations belong in the weblate/ catalogs, not in the generated locales/ modules."
+            exit 1
+          fi
+
   fonts:
     runs-on: ubuntu-24.04
     timeout-minutes: 10