See developer documentation at:
https://gramps-project.org/wiki/index.php?title=Portal:Developers
https://gramps-project.org/wiki/index.php?title=Brief_introduction_to_Git#Making_a_patchfile
https://gramps-project.org/wiki/index.php?title=Brief_introduction_to_Git#Making_a_PR

If you are interested in translating:
* The Gramps program to your language see:
https://gramps-project.org/wiki/index.php?title=Translating_Gramps
https://gramps-project.org/wiki/index.php?title=Portal:Translators

* The Gramps user manual to your language see:
https://gramps-project.org/wiki/index.php?title=Translating_the_Gramps_User_manual