Is april a good month to visit taiwan? Can language be a barrier if we don't speak chinese?

Yes, April is a great time for a visit. It will be cloudy and rains lightly sometimes. The temeprature is moderate and the scenery is quite beautiful.

Don't worry about the language. There are clear English guiding signs in the airport, metro stations, etc. The locals can speak some simple English, too. They are very friendly to you. Have a nice trip!