

Depends on the context, commenting in your native language is often totally okay.
Let’s say: a Japanese artist posting an art with Japanese caption, they would totally happy to receive comment from various language, displaying a cultural exchange.
This behaviour of native language comment is actually common in Asia and Africa, but not in Western countries…
Just be wary of joke or sarcasm that might interpreted as hate comment.
Using English is totally okay!
I did it all the time and we interacted just fine.
Using machine translation can lead to mistranslation, even your heartwarming comment can be interpreted as hostile.