Serbo-Croatian.
Leaning the language in the Latin alphabet is sufficient, but if you want to be thorough, I suggest also learning the Cyrillic alphabet as well. You will find mixed use of the alphabets here, even so far as seeing street signs in one alphabet on one corner, and the other alphabet on the opposite corner.
To avoid finding yourself in the middle of nationalistic arguments with Montenegrins, I suggest you refer to the language as "Lokalni" (Local Language) in conversation.