Normally Thais don't speak other languages (particularly diplomatic staff who get rotated to a different post every few years).
So, it would be a case of any local staff who are stationed there but I would generally not recommend submitting documents in any languages other than Thai or English.
Where I applied, I spoke with the locally engaged staff in Chinese (their native language) but even though I presented documents in Chinese (which they could understand) this was not permitted, so I had those documents translated ahead of time (I communicated with the consulate prior to my arrival).
Thais who live or work abroad almost always speak English (as opposed to those who live here and have never been abroad).
Sometimes, documents presented in Thailand for official purposes need to be in Thai only but for foreigners and extensions at immigration offices inside the country, English is accepted as well.
Anonymous participant There you go, just do a border run. You know already that IF an extension is needed, you'll need to present documents in Thai or English plus whatever else they're asking for.
If they require all the same documents as for the initial visa application, then a border run might be a lot easier.
Well yes, car parking at immigration offices anywhere in the country (except for tiny little offices such as Mae Hong Son) can be a pain. However, at most offices, even the smaller ones, it can still take around an hour or longer to accomplish a simple task like applying for a re-entry permit even if no other people are waiting. I've had plenty of personal experience in this arena, helping my colleagues from Europe and China. Even Nakorn Sawan, Mae Sot and Mae Hong Son (although Mae Sot shouldn't be underestimated as they can get very busy).
Mae Sai was super busy and took more than 2.5 hours.
Anonymous participant My DTV was approved without incident but I knew how to follow the rules and common sense should tell you that when dealing with Thai officialdom, you present documents in Thai or English.
Do you speak German with Thais in Thailand? Come on now.
I've not seen one consulate accepting languages other than Thai or English though. I looked long and hard and couldn't find one, but I didn't make a big deal about it. I got my documents in French and Chinese, translated into English.
It's highly recommended documents are in Thai or English, particularly if needing to extend this visa. Documents in any other language are useless and immigration won't accept them. Thais don't speak German, Dutch, French or whatever.
For better or worse, English is the only global language.