Godot's translation work is coordinated on Hosted Weblate, an open source web-based translation platform, where contributors can work together on translations using various internationalization features. Creating an account there is free, and you can also login directly with your GitHub, BitBucket, Google or Facebook account.
To avoid merge conflicts when syncing translations from Weblate (currently this is done manually), we ask all contributors to work there instead of making pull requests on this repository.
Link if you missed it: https://hosted.weblate.org/projects/godot-engine/godot
If you want to translate for a language which is not featured yet on Weblate, you can add it (when logged in) by clicking the "Start new translation" button at the bottom of the page.
Alternatively, you can use this direct link.