How does an exchange student go to another country for a year when the language of education is different? Doesn't the exchange student attend any lecture or course during the visit?
Except for negligible exceptions, the language of education is the local language, and almost every country has a different language.
I feel the comments/answers are based on the large countries (e.g., many students can speak German or French). Consider small countries like Latvia, Estonia, etc. I doubt anyone learns those languages unless you already have a connection (e.g., a parent is from there, philology student). I think the purpose of exchange projects is to stay in/experience places you normally don't.
I doubt if basic language skills learned in school is sufficient for understanding a course/lecture.
If your choice is based on the language you speak, (formerly the UK), Ireland, (possibly The Netherlands) should be flooded with exchange students (or at least demands).
As a side note, I read somewhere (I will look for it), the popular destinations for Erasmus students are cities with beaches regardless of the country's language or the university's reputation. A popular destination country is Turkey.
I believe Erasmus is a cultural programme rather than an educational one. My question is how education quality assurance is managed/guaranteed.