Going to a McDonald's in Luxembourg it was quite amusing to see one person take on 4 orders in 4 different languages back to back. (English, Dutch, German and French)

On another note while most Luxemburgers will speak 4 or more languages, most people I spoke to wouldn't respond if you didn't speak the language they find "native" to their area. Until you then start speaking another one of the languages and they understand you're just a tourist trying to speak one of their languages.