If you think that Spanish or Castilian is the language of Spain, you're only partially right.
True, Spanish is the national language and the only language you can use if you want to be understood almost everywhere. But Spain also has three other officially recognized languages, and language use continues to be a hot political issue in parts of the country. In fact, about a fourth of the country's residents use a tongue other than Spanish as their first language. Here is a brief look at those languages:
Euskara: Euskara is easily the most unusual language of Spain — and an unusual language for Europe as well, since it doesn't fit in the Indo-European family of languages that includes Spanish as well as French, English and the other Romance and Germanic languages.
Euskara is the language spoken by the Basque people, an ethnic group in Spain and France that has its own identity as well as separatist sentiments on both sides of the Franco-Spanish border. (Euskara has no legal recognition in France, where far fewer people speak it.) About 600,000 speak Euskara, sometimes known as Basque, as a first language.
What makes Euskara linguistically interesting is that it has not been shown conclusively to be related to any other language. Some of its characteristics include three classes of quantity (single, plural and indefinite), numerous declinations, positional nouns, regular spelling, a relative lack of irregular verbs, no gender, and pluri-personal verbs. The fact that Euskara is an ergative language (a linguistic term involving cases of nouns and their relations to verbs) has caused some linguists to think that Euskara my have come from the Caucasus region, although the relationship with languages of that area hasn't been demonstrated. In any case, it is likely that Euskara, or least the language it developed from, has been in the area for thousands of years, and at one time it was spoken in a much larger region.
The most common English word that comes from Euskara is "silhouette," the French spelling of a Basque surname. The rare English word "bilbo," a type of sword, is the Euskara word for Bilbao, a city on the western edge of Basque Country. And "chaparral" came to English by way of Spanish, which modified the Euskara word txapar, a thicket. The most common Spanish word that came from Euskara is izquierda, "left."
Euskara uses the Roman alphabet, including most letters that other European languages use, and the ñ. Most of the letters are pronounced roughly like they would be in Spanish.
Catalan: Catalan is spoken not only in Spain, but also in parts of Andorra (where it is the national language), France and Sardinia in Italy.
Catalan looks something like a cross between Spanish and French, although it is a major language in its own right and, some say, may be more similar to Italian than it is to Spanish. Its alphabet is similar to that of English, although it also includes a Ç. Vowels can take both grave and acute accents (as in à and á, respectively). Conjugation is similar to Spanish's.
About 4 million people use Catalan as a first language, with about that many also speaking it as a second language.
Galician: Galician has strong similarities to Portuguese, especially in vocabulary and syntax. It developed along with Portuguese until the 14th century, when a split developed, largely for political reasons. For the native Galician speaker, Portuguese is about 85 percent intelligible.
About 4 million people speak Galician, 3 million of them in Spain, the rest in Portugal with a few communities in Latin America.
Miscellaneous languages: Scattered throughout Spain are a variety of smaller ethnic groups with their own languages, most of them Latin derivatives. Among them are Aragonese, Asturian, Caló, Valencian (usually considered a dialect of Catalan), Extremaduran, Gascon and Occitan.
Euskara: kaixo (hello), eskerrik asko (thank you), bai (yes), ez (no), etxe (house), esnea (milk), bat (one), jatetxea (restaurant).
Catalan: sí (yes), si us plau (please), què tal? (how are you?), cantar (to sing), cotxe (car), l'home (the man), llengua, llengo (language), mitjanit (midnight).
Galician: polo (chicken), día (day), ovo (egg), amar (love), si (yes), nom (no), ola (hello), amigo/amiga (friend), cuarto de baño or baño (bathroom), comida (food).