The game doesn't support adding your own font yet unfortunately.
Did you translate it yourself? That'd be extremely fast! If you wouldn't mind sharing the file with me, I can make sure the next update has a font that is compatible.
Viewing post in Amelia's Stranded Adventure comments
Are you able to join my Discord server and keep up communications with me? I could make a special build of the game for you that will have a Font you can use, but I will need to know which language you're working on. If any issues arise, it might help you to have a more direct line of communication with me too.
Link to Discord can be found on the Main Menu > Support the dev and Social.