Hi @NiclAss it’s possible only if you’re the owner of both projects. In this case use “shared TM” option in Resources → TM.
If owner is another person, regardless of project visibility type TM can’t be shared. As a result, you’ll need to ask this person to share the TM with you manually let’s say once per week, and so you will share yours TM with this person by email or so.
We don’t have such plans as far as TM is intellectual property. I know that some teams have a stand-alone repository with translations, you can ask the original owner to invite you as admin so you would be able to manage both modification and the original game version.