Mastodon has an optional translation system to translate posts in languages that you don't speak. To use it, just click on "Translate" below a post (on some apps the translate option may be in the post's ⋯ menu).
I've tried to answer common questions about Mastodon's translation feature in this guide:
➡️ https://fedi.tips/is-there-a-built-in-language-translation-system-on-mastodon
Let me know in the replies if I've missed your question.