[ACS-12385] Fix en-AU collision (#5330)

* [ACS-12385] Fix en-AU collision

* [ACS-12385] remove comments

* [ACS-12385] Diff by SHA instead of a remote-tracking branch name

.github/workflows/pull-request.yml

@@ -79,6 +79,30 @@ jobs:
             echo "only-e2e-changes=true" >> $GITHUB_OUTPUT
           fi
 
+  protect-en-source:
+    name: 'Validate / Protect English source (en.json)'
+    if: ${{ github.event_name == 'pull_request' && github.head_ref == 'automated-translations-update' }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v7
+        with:
+          fetch-depth: 0
+
+      - name: Fail if automated Crowdin PR modifies en.json
+        env:
+          BASE_SHA: ${{ github.event.pull_request.base.sha }}
+        run: |
+          git fetch --no-tags --depth=1 origin "$BASE_SHA"
+          CHANGED_EN=$(git diff --name-only "$BASE_SHA"...HEAD | grep -E '(^|/)i18n/en\.json$' || true)
+          if [ -n "$CHANGED_EN" ]; then
+            echo "::error::Automated Crowdin PR must not modify the English source (en.json). Offending file(s):"
+            echo "$CHANGED_EN"
+            echo "This usually means a Crowdin target language (e.g. en-AU) collides with the 'en' two_letters_code. Fix crowdin.yml languages_mapping instead of merging this change."
+            exit 1
+          fi
+          echo "OK: no en.json source file modified by the automated Crowdin PR."
+
   build:
     name: 'build'
     runs-on: ubuntu-latest