title is the translated title in whatever language you're requesting, and original_title is the original title.

title and original_title are producing the exact same results.

the first example below is supposed to be sorted by title, but instead appears to be sorted by original_title (as the alphabetization is completely off in english).
Comparing this to the results for original_title sorting, they're an exact match.

sort_by title.desc:

https://api.themoviedb.org/3/discover/movie?api_key=apikey&vote_count.gte=10&sort_by=title.desc&watch_region=CA&language=en&with_genres=37&page=1  

sort_by original_title.desc:

https://api.themoviedb.org/3/discover/movie?api_key=apikey&vote_count.gte=10&sort_by=original_title.desc&watch_region=CA&language=en&with_genres=37&page=1