If you’ve ever watched anime without dubs where they have to speak English a lot, you’d know lol. Generally IIRC they just have to sound believable enough.

Non animated example: Stargate SG1 did this once and the spoken dialogue was an inside joke., Reportedly, their Russian was terrible since they just used English-speaking extras - not that most English speakers would know. Basically just a couple of Russian soldiers on duty heard a noise, ones asks “what was that?” And the other answers something like “probably just the monster from the end of last season.” Then the subtitles have the correct dialogue.