use Babel to compile localizations and include in source tarball

python3-babel was also included in the gitlab-ci docker image:
ffc08dbc1d

setup.cfg

@@ -1,3 +1,37 @@
 
 [aliases]
-release = register sdist upload --sign
+release = register compile_catalog sdist upload --sign
+
+# All this below is for Babel config.  Ideally we would only use
+# Babel, but it is still missing some key features that gettext gives
+# us.  So for now, this Babel setup is just to make it easy for Python
+# people who are used to it.  Babel is missing:
+#
+# * properly tagging various Python formats in the comments
+# * --add-location=file
+# * --join-existing
+# * --sort-output on update
+#
+# So for now the canonical way to update the template and translation
+# files is: `make -C locale`
+
+[extract_messages]
+keywords = _
+charset = UTF-8
+sort_output = true
+no_location = true
+add-comments = true
+output_file = locale/fdroidserver.pot
+msgid-bugs-address = https://gitlab.com/fdroid/fdroidserver/issues
+
+[update_catalog]
+output_dir = locale
+input_file = locale/fdroidserver.pot
+
+[init_catalog]
+input_file = locale/fdroidserver.pot
+output_dir = locale
+
+[compile_catalog]
+domain = fdroidserver
+directory = locale