The principal and official language of Germany is German, an Indo-European language. Standard High German is used for official, educational, and literary purposes. Spoken German, however, differs from High German in the form of dozens of distinctive dialects and simplified street usage. One version, Low German, or Plattdeutsch, resembles Dutch and is spoken in the seaboard areas of the northwest. Southern dialects such as Swabian and Bavarian may be hard to understand for North Germans or for foreign visitors who learned only High German in school. There are small language minorities, such as the Sorbs of southeastern Brandenburg and the Danes of northern Schleswig-Holstein; both of these groups also have some cultural autonomy. The various immigrant populations also retain their separate languages, such as Turkish, Greek, Italian, Spanish, and Serbo-Croatian. However, the public schools insist that all children learn German.