Luffy appears in Gintama

I might try reading this since I couldn't get into the anime every time I tried.

The translation quality varies (same for the anime really. Only site I found with the old fansubs, which in most people's opinion is better than the Crunchyroll subs is here https://www.animegg.org/gintama-episode-3 ). The voice acting and anime-specific jokes are good and some jokes are probs enhanced animated (eg Gintoki being stuck in sleep paralysis ep 47, which is just voice acting with him stuck in bed, tho I've not read the manga chapter to compare). Fanslators "Hi wa mata noburu" supposedly did a good translation but only from around chapter 285 (it's one of the ones on mangadex).
Defo helps to know what you're getting into. It's mostly comedy with glimpses of seriousness or wisdom in most episodes and then the occasional serious arcs that reverse that.