configures "l10n" GitHub Actions workflow for nightly translation sync

.github/workflows/l10n.yml

@@ -0,0 +1,30 @@
+name: l10n
+on:
+  # Run nightly at midnight UTC.
+  schedule:
+    - cron: "0 0 * * *"
+  # Also allow manual invocation.
+  workflow_dispatch:
+
+jobs:
+  update-translation-catalogs:
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Check out securedrop-client
+        uses: actions/checkout@v2
+      - name: Set Git identity
+        run: |
+          git config user.name github-actions
+          git config user.email [email protected]
+      - name: Set up Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: 3.7
+      - name: Install dependencies
+        run: pip install --require-hashes -r requirements/dev-requirements.txt
+      - name: Update translation catalogs
+        run: make update-translation-catalogs
+      - name: Update list of supported languages
+        run: make supported-languages
+      - name: Push
+        run: git push