Do you know a human language? Do you want Mastodon to be available in that language? There's this website where you can look at English words and phrases and put your language's words and phrases into it and save it and then it'll end up in the next Mastodon release. Probably in 3-4 days max. That website is:
https://weblate.joinmastodon.org
There are some languages that have an awful lot missing. Like Hungarian and Finnish.