Well there's no reason why it shouldn't be part of the git repository. The crucial point is to separate the part of your project which is versioned from the part which can be released at any moment.
Typically to do this, you'd put it in its own folder and it would have its own lifecycle and continuous integration. I'm guessing in your case it would be a simple jar with .properties files for your resource bundle. Then everytime you need to package a new version of your program, you compile a specific version, and you grab the latest compilation of your unversioned folder and put them together for distribution, probably as a referenced library of your web application.
In this way, you always have a copy ready for distribution of the unversioned binary and also the possibility to combine with versioned binary for distribution as well. It may be in your best interests to have the default .properties file in your project directly, so that you can test the web application without requiring the bundle (you would simply not have translations available in that case).
If you prefer, you can put this in a separate git repository, but I think that is a little overkill, considering the two components are halves of a whole program. Good luck!