I asked the language school if they would be okay with me answering questions like yours....they had no problem at all....BUT , they were concerned...due to all the negative comments on this site and other visa sites stating categorically that language is not a soft power option, that staff at the embassy in London may have some comeback.
From comments on here it appears I am the only person in the world that got DTV based on learning Thai language . So I hope you understand my reluctance to divulge the school.
Having said that, all I did was Google language schools in Bangkok...if you go this route make sure the school has a government licence/approval.
I didn't make the rules either ! I have a DTV visa issued by the Thai embassy in London based on me enrolling on a course to learn the Thai language at a language school....simple.