"Is it really true that everyone can communicate in Taiwanese?" Virtually all the people born and raised in Taiwan can use Taiwanese; even if they can't speak it well, they can certainly understand it.
在台灣「生于斯、長于斯」的男女老少，幾乎都能聽、會講閩南語；就算有不會講的，他們至少也聽得懂。