Add workflow to auto-import Weblate changes

If the Weblate GitHub user opens a PR, this will import the Weblate translations in that PR into the prelude, then export them, then create a diff of the changes that is used to add a commit to the PR's branch containing those changes.

The export is done because Weblate just appends new translations to its YAML files, but they're otherwise sorted alphabetically and the export is a way of doing that.

.github/workflows/import-translations.yml

@@ -0,0 +1,48 @@
+name: Import translations from Weblate
+
+on: [pull_request]
+
+jobs:
+  import:
+    runs-on: ubuntu-20.04
+
+    # Only run if the pull request was opened by Weblate's GitHub bot user.
+    if: ${{ github.event.sender.id == 1607653 && github.event.pull_request.maintainer_can_modify == true }}
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.10'
+
+      - name: Install dependencies
+        run: |
+          python -m venv .venv
+          ./.venv/bin/activate
+          pip install -r requirements.txt
+
+      - name: Run import translations script
+        run: python scripts/import-translations.py
+
+      - name: Run the export translations script
+        run: python scripts/export-translations.py
+
+      - name: Create patch containing changes
+        run: git diff > sync-translations.patch
+
+      - name: Record pull request head data
+        run: |
+          echo 'export PR_HEAD_URL="${{ github.event.pull_request.head.repo.clone_url }}"' > git_vars.sh
+          echo 'export PR_HEAD_REF="${{ github.event.pull_request.head.ref }}"' >> git_vars.sh
+          echo 'export COMMIT_MESSAGE="Import translations from Weblate"' >> git_vars.sh
+
+      - name: Upload data
+        uses: actions/upload-artifact@v4
+        with:
+          name: sync-translations-data
+          path: |
+            sync-translations.patch
+            git_vars.sh