I don’t know specifically about animation humor but some general language based things will not easily translate from English to Japanese.

• As far as I can tell, Japanese people swear a lot less and their assortment of swearing is quite limited compared to English. I think creative swearing, which is quite common in media, is very hard to translate to Japanese.
• Japanese poetry is very different and it doesn’t really rhyme in the way we are used to. Translating something that rhymes into Japanese is probably a challenge.

I’m not fluent at all so don’t take my word for it.