The official language, like the rest of Denmark,is Danish. English is also widely understood
Ærø can be reached by ferry from Svendborg, Funen.
Be careful if asking directions, as it's fairly critical to get the pronunciation right in order to be understood. If you ask people for the way to Aero, they will likely look puzzled and point you to the nearest airport after some thinking. If you have trouble; include island in the question (i.e. How do I get to Aero island?).