I guess streamingis OK, but with local services. Some do have English subtitles, though interestingly that is a recent developmnet.
As to video rental, there are a few, but the problem is that most DVDs produced in Taiwan do not have English subtitles at all. Hong Kong versions do. So newer movies are less likely to have English subtitles.
Regarding the old stuff, I have a collection of classics and to this day, getting City of Sadness in English is one of my quests … there are versions out there, just too expensive.
Currently, there are several boxed DVD collections for Hou Hsiao-hsien and Ang Lee´s early works, plus most classics of Taiwan´s New Wave/New Cinema directors are available with English subtitles. Not expensive.
If all else fails, may I recommend a membership to the Cinema Archives? Located in Tsingdao Road -the road in front of the Legislative Yuan- it is a treasure trove of movies. You can watch them there though.