hey there - thanks for your question! i'm not familiar with DeepL specifically, but if it uses genAI / LLMs for translation then i'd ask that you please not use it as part of your submission.
non-english games are very welcome (in fact I see the jam has already received a few submissions in other languages) so please do consider submitting a japanese game if you'd like to participate! <3
also, another thing you could do is make a post on the bitsy forum (https://ledoux.itch.io/bitsy/community) to see if anyone would be willing to help you translate the game into english - i know there are some japanese-english translators in the community, so maybe someone would be up for collaborating!