I have been using Flask Babel to run a multilingual app for couples of month now. It was working fine until late September. It is working fine locally but when pushed to the GAE, the translation is not working. GAE is storing every version pushed and I was able to went back to version where the translation was working, made sure the configuration was exactly the same but it's still not working.
I made sure the messages.po is pushed and use the tag --verbose=info to make sure it's pushed and indeed I can see the sourceUrl and the sha1Sum of the file in the cloud storage.
I checked that the path translations/en/LC_MESSAGES match the local on babel 'en'