OT but I can actually say that in Spanish: El espanol es un idioma tan divertido!
Yes, that works well! The only thing would be is that "tan" means "so" in the context of as a comparative. If you were comparing it to another language like English, then you could use tan. If not, you can use "muy" (translates to "very") without comparing anything.
For example, this is the correct way to use tan:
Español: "El español no es tan fácil como el inglés."
English: "Spanish isn't as easy as English."
Since you aren't comparing anything in your sentence, you would just take your original sentence and replace "tan" with "muy"
Your original sentence in Spanish: "El espanol es un idioma tan divertido!"
Correction: "El espanol es un idioma muy divertido!"
English: Spanish is a very fun language!
And then mucho is a whole other story lol