Algeria's official language is Arabic, which is spoken by an estimated 81% of the population. All official documents are printed in Arabic and those from non-Arab households usually learn the language in school. Arabic has been the official language of the country since 1963. More recently, Berber has become recognized as one of the country's national languages. This occurred in 2002 and is an appropriate step since 99% of the population speaks Arabic, Berber or both. Although being introduced in French-colonial times, and still often taught in schools and used in government and higher education, French has no official status in Algeria. While a large majority of the country can understand the language, it is estimated that only about 20% can read and write it.
Algerian Arabic is somewhat different to the Arabic commonly spoken in other parts of the world. The language has been greatly influenced by Berber, Turkish and French from which it has many borrowed words. It also has a much more simplified vowel system. There are quite distinct local variations of Arabic in the various parts of Algeria. Though there are many different Berber dialects, they are all grouped under the same name. Only about 19% of the population speaks Berber but the language is so widespread that you are likely to encounter it virtually anywhere in the country. Algerian Sign Language is widely used by the deaf community in the country and is sometimes seen on national TV.
Times gone by have seen the inhabitants of the country speak Phoenician and Turkish though both languages are no longer in use here. There are a number of other African languages that exist in the country, but these account for a very small portion of the population. If you visit Algeria, you might find it helpful to speak French, which is at least understood by many Algerians. Failing that, you will likely be able to arrange a translator or tour guide who can speak one or more foreign languages and who will help you communicate with the locals.