Hey. I downloaded the quark mod to github and I'm trying to upload my translation (to hebrew). How can I contribute this?

Start by clicking that Fork button up on the top-right to create your own copy of the Quark Repository to work with.
Modify (or create) the lang file you wish to contribute translations to, and upload them to your own repository. When you're done with that, open a pull request and we'll review and merge it in.

Thanks for contributing!