The main language spoken is, unsurprisingly, Czech. Slovak is often heard as there is a large Slovak minority and the two languages are mutually intelligible to a certain extent. Czechs are very proud of their language, which is why you won’t find many signs in English even in Prague (outside the main tourist areas). Many older people, especially outside the main cities, are also unable to converse in English, so it’s a good idea to learn some Czech or Slovak before you arrive. However, most young people speak at least some English, as it has been taught in most schools since 1990.
Most Czechs speak a second and often a third language. English is the most widely known language, especially among young people. German is probably the second most spoken language among older people. Russian was compulsory in all schools under the communist regime, so most people born before 1975 speak at least some Russian (and often quite well). However, the association with the communist era and the Soviet invasion of 1968 (and today’s Russian-speaking criminal gangs) has given the language some negative connotations. It is also not very useful among young people as, contrary to popular belief, it cannot be understood with Czech (apart from some similar words and simple sentences) and has been largely displaced by English as the foreign language of choice. Other languages, such as French or Spanish, are also taught in some schools. It is also possible to understand some basic words or simple sentences in other Slavic languages (Polish, Bulgarian, Serbo-Croatian, etc.).
The Czech and Slovak languages are very difficult for English speakers to understand because, like their sisters, they can be linguistically convoluted languages (especially Czech) and take time and practice to master, especially if you are not really familiar with other Slavic languages, including Russian. However, if you can learn the alphabet (and the corresponding letters with accents), pronunciation is easy because it is always the same – Czechs and Slovaks pronounce each letter of a word with the accent falling on the first syllable. Combining consonants in some words may seem incredibly difficult, but it’s worth it!
The Czech language has many local dialects, especially in Moravia. Some dialects are so different that they can sometimes be misunderstood even by a native Czech from another region. However, all Czechs understand standard Czech (as spoken on TV, written in newspapers and taught in schools) and should be able to speak it (but some are too proud not to use their local dialect). Some even cannot speak standard Czech, but can write it correctly.
The Czech and Slovak vocabularies are similar, with some words not included. The young generation born after the dissolution of Czechoslovakia is separating in both countries and they have problems understanding each other.