The official language of Croatia is Croatian (Hrvatski). Croatian is a Slavic language that arrived in the Balkans region with the migration of the Slavs in the 6th or 7th century. The language eventually evolved, under the influence of the Bulgarian, Slovene, Serbian and Croatian languages.  Throw in the language of the Ottomans, Venetians, Hapsburgs, and  Italians, and you are left with a language that is the amalgam of its history.

The primary difference between Croatian and Serbian is that Croatian is written in the Roman alphabet while Serbian is written in Cyrillic. Linguists consider Croatian, Serbian and Bosnian the same language but political differences among the groups makes this a controversial point. Croatians, Serbians and Bosnians generally do understand each other when they speak.

Nearly all Croatians speak at least one other language. In the north, that second language is likely to be German while along the coast, it is likely to be Italian. Tri-lingual Croatians are not rare. English is widely although not universally spoken. Anyone working in the tourist business in any way will have mastered some English and for young people English is now the second language of choice.     
 
Mastering at least a few words of Croatian is a must in order to assimilate, although speaking Croatian is not a simple matter. Croatian grammar is complicated but the pronunciation is fairly straightforward. Every letter is pronounced and the accent usually falls on the first letter of every word.