You should choose a university abroad that fits your interests for your master thesis. The FU Direktaustausch program cooperates with five different universities in Latin America and allows an easier access. This direct exchange program also includes that you don't have to pay any tuition fees at the university abroad. The Latin American Institute has a cooperation agreement with more universities, however those are not free of tuition. You can also organize an exchange on your own at any university you want but keep in mind that you might have to pay fees and that the communication might be more difficult.