This can go both ways whether you understand both the original dub and the subtitle language that differs from the dub, for example: I recall watching a TV show episode where a conversation about a friend of theirs being drafted to war, but this piece of dialog was horribly translated: “He’s still a kid” as in the guy is his early 20s.
The subtitles in 日本語 however, used the worst wording for this idiomatic prasing by translating “kid” as in a literal minor (子供) when the real context is more on referring to someone who’s 20 years old or above (basically equivallent to saying “young man” / 若い人) which butchered the scene since the subtitles failed to express that.
I mean, do you know examples of a movie or TV show where the subtitles suck at translating the spoken dialog when it involves idioms, puns or even cultural references? Whether it’s French Dub & English Sub or vice versa (like English Dub > Spanish Sub & etc.) since each language has their own way of conveying a message.
Yeah, Japanese subtitles can have issues. Various broadcasters have been caught saying something else, though usually only when they overdub so one can barely hear the actual person.