As a Southerner who would definitely say "I might could…", I would never say “I didn’t necessarily could speak it well”. That’s not how double modals work. (“I used to could…” seems marginally ok to me though.)
Also the “needs fixed” thing is not a Southern dialect property, I associate it more with like Pittsburgh.
Also the “needs fixed” thing is not a Southern dialect property, I associate it more with like Pittsburgh.