I just dive in and learn as I go by looking at the rest of the code-base and familiarizing myself with their chosen patterns, language documentation, and trial

I just dive in and learn as I go by looking at the rest of the code-base and familiarizing myself with their chosen patterns, language documentation, and trial + error. Core principles remain mostly the same regardless of language, and anything that's not the same is pretty quick to pick up with background knowledge of peripheral technologies and Google.