Can I write the language specific summary of my thesis in dialect? My mother tongue is Dutch and I'm writing my thesis in English. I am required to write a summary both in English and my own language, Dutch. Would it be ok to write the Dutch summary in a dialect? Which is still comprehensible to everybody, just slightly different spelling. I have a deep connection to my dialect which is dying out. My thesis does regard natural language but has no relation to dutch or dialects or anything of the sort.

I can't ask my uni because there are 0 guidelines to structure or style, just content. And it is very very strict on the size of a thesis, only allowing 6000 words which is ridiculously small for 8 months of work.
Not asking your university because there are no guidelines makes no sense. Since there are no guidelines, you should ask your university. Not random strangers online. They are the only ones who can answer. Ask your advisor too. If both tell you they don't care, do what you want. If one of them has some requirement, do what they say.