No, they are not usually written except people sometimes doing it casually in social media, but because our lettering system is almost fully phonetic, it is very easy to write and read them if you just speak finnish. Also if you are native speaker, you kind of learn the certain fluidity in the core of the language, so you can pretty much understand the words even if they vary a lot (except people from Rauma, nobody understands them).

I really thought it would have been cracked by AI because it can translate finnish pretty accurately (not always...) and if you can do that dialects aren't hard at all, but I was surprised to find that it still cannot! I am assuming it really is just because there are not enough written sources to teach from.

//Oh, and as a summary my main points were, that AI most definitely has not "solved" learning and translating languages as it yet cannot even translate a lot of things, and I guess also, that you cannot trust AI translations if the text translated is some obscure language you do not know. They can sound convincing and form coherent sentences, but the meaning can be fully incorrect.