Mariachis are traditional musicians. Mariachi music originated in the state of Jalisco during the 19th century, when the Mariachis played music at weddings. the word Mariachi originated from the French word marriage. Mariachis are still engaged for Mexican weddings.
Ok, so the principal language in Mexico is Spanish, however it is called Mexican Spanish as some of the words and the dialect is slightly different than Spanish.
Dont fret if you dont speak the language, their English is very good, but they do appreciate it if you try a little.
I bought this Rough Guide to Mexican Spanish, it came in really useful.