>>76493Mi Nam dialect is actual Taiwanese dialect, along with some other variations i.e Hakian & mountain talk.
Mandarin is a language that has been adapted via China and is probably the best way to communicate with people of the younger generation.
As for Japanese, there are a few elderly people that speak that natively due to the occupation of Japan during earlier wartimes.
If your looking for something to do, there's parks, shrines, temples, lakes, hot springs, monuments(shitload of those) and some techie stuff in Taipei.
I recommend heading up north to "Magong", it's a resort town that many locals travel to relax. Mostly beaches and lots of activities if you enlist a tour group.
English is not a very popular language so I suggest you either hire a guide or find a local friend to take you around. Even though, there are signs in English it's mostly gibberish translations(making it pointless, since the locals won't understand a word of it).
I'd say Taipei is probably where most of the English speaking population exists. Everywhere else, you'll have a hard time finding someone who'll understand a speck of English. Or you could hang by one of those English schools, might find a local that's interested in learning and exchange languages.