Add translation .po file checks

.github/workflows/build.yml

@@ -148,3 +148,17 @@ jobs:
 
       - name: Run ${{ matrix.toxenv }}
         run: python -m tox -e ${{ matrix.toxenv }}
+
+  translations:
+    name: Check Translations
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Git clone
+        uses: actions/checkout@v2
+
+      - name: Install dependency
+        run: sudo apt install -y gettext
+
+      - name: Compile translations
+        run: for po in po/*.po; do msgfmt -cv --statistics -o - ${po} >/dev/null; done

doc/translations.md

@@ -13,6 +13,10 @@ is equivalent to:
 
 ``linkchecker/po $ make``
 
+Translation progress and validity can be monitored with:
+
+``linkchecker/po $ make check``
+
 Man Page Translations
 ---------------------
 

po/Makefile

@@ -27,8 +27,13 @@ $(TEMPLATE): $(POSOURCES)
 	  --msgid-bugs-address=$(MYMAIL) -o $(TEMPLATE) \
 	  --keyword=_n:1,2 $(POSOURCES)
 
+check:
+	@for po in $(POFILES); do \
+		$(MSGFMT) -cv --statistics -o - $$po >/dev/null; \
+	done
+
 clean:
 	@for f in $(LANGUAGES); do rm -f $(LDIR)/$$f/$(LFILE); done
 	rm -f *.mo *.bak
 
-.PHONY: clean
+.PHONY: check clean