Latgalian language
Originally Latgalians were a tribe living in modern Vidzeme and Latgale. It is thought that they spoke the Latvian language, which later spread through the rest of modern Latvia, absorbing features of the Old Curonian, Semigallian, Selonian and Livonian languages. The Latgale area became politically separated during the Polish–Swedish wars, remaining part of the Polish–Lithuanian Commonwealth as the Inflanty Voivodeship, while the rest of Latvians lived in lands dominated by Baltic German nobility. Both centuries of separate development and the influence of different prestige languages likely contributed to the development of modern Latgalian as distinct from the language spoken in Vidzeme and other parts of Latvia.
Latvian language
Latvian belongs to the Baltic branch of the Indo-European language family. It is one of two living Baltic languages with an official status (the other being Lithuanian). The Latvian and Lithuanian languages have retained many features of the nominal morphology of the proto-language, though in matters of phonology and verbal morphology, they show many innovations, with Latvian being considerably more innovative than Lithuanian.