Obviously, it kind of depends where your friend wants to study and what your friend intends to study.
English is something of a universal language, so even in countries where it's not the official language, knowing a little English can help you out almost anywhere.
If your friend intends to study in an English-speaking country then it'd be a good idea for him to learn some English regardless of his course of study. He'll need enough English to get by in daily life and in order to enjoy his stay abroad.
If his course requires high levels of communication, then he'll obviously need to have mastered English to a level where he can partake in learning and the haring of information.
On certain courses, your friend may not even be accepted on the course or be able to obtain a visa allowing him entry into the country unless he is able to prove that he can communicate in English at the required level.
Luckily, there are many courses and resources available - both online and offline, free or paid for - which will help your friend learn English.
Even posting questions and answers on Blurtit could be considered good practice!