Should be fairly easy to accomplish. Thankfully, Minecraft has native translation support. Translation keys are already implemented and working in the mod - just need to continue adding them along with getting people to translate.

If you want to translate
See the default English files: https://gitlab.com/SamB440/tale-of-kingdoms/-/blob/master/src/main/resources/assets/taleofkingdoms/lang/en_us.lang and https://gitlab.com/SamB440/tale-of-kingdoms/-/blob/master/src/main/resources/assets/taleofkingdoms/lang/en_us.json

Fork the repository by clicking the big fork button at the top right on the main page: Fork it

Create, or edit the files in the lang folder (https://gitlab.com/SamB440/tale-of-kingdoms/-/blob/master/src/main/resources/assets/taleofkingdoms/lang/)

If you want to develop
Found a place where there should be a translation key? Fork the repository, make your changes, and create a merge request.

Currently considering whether to change the text from the original mod to make more sense, as the English from the old mod is not that great.