Add PR labeler action to label translation-related PRs (#845)

* Add PR labeler action to label translation-related PRs

* Sync labels when PR changes

* Update instructions for new translation

.github/labeler.yml

@@ -0,0 +1,47 @@
+translation:
+- po/**
+
+'translation/bn':
+- po/bn.po
+
+'translation/da':
+- po/da.po
+
+'translation/de':
+- po/de.po
+
+'translation/el':
+- po/el.po
+
+'translation/es':
+- po/es.po
+
+'translation/fr':
+- po/fr.po
+
+'translation/id':
+- po/id.po
+
+'translation/it':
+- po/it.po
+
+'translation/ja':
+- po/ja.po
+
+'translation/ko':
+- po/ko.po
+
+'translation/pt-BR':
+- po/pt-BR.po
+
+'translation/ru':
+- po/ru.po
+
+'translation/tr':
+- po/tr.po
+
+'translation/zh-CN':
+- po/zh-CN.po
+
+'translation/zh-TW':
+- po/zh-TW.po

.github/workflows/labeler.yml

@@ -0,0 +1,14 @@
+name: "Pull Request Labeler"
+on:
+- pull_request_target
+
+jobs:
+  triage:
+    permissions:
+      contents: read
+      pull-requests: write
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/labeler@v4
+      with:
+        sync-labels: true

TRANSLATIONS.md

@@ -89,6 +89,13 @@ header (the first entry with `msgid ""`) to the correct language.
 > translations will be wrong after this, so you must inspect them by hand
 > afterwards.
 
+Next, please update the file `.github/labeler.yml` to include the new language:
+
+```diff
++ 'translation/xx':
++ - po/xx.po
+```
+
 ### Updating an Existing Translation
 
 As the English text changes, translations gradually become outdated. To update