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.
Lithuanian language
Lithuanian is one of two living Baltic languages, along with Latvian. An earlier Baltic language, Old Prussian, was extinct by the 18th century; the other Western Baltic languages, Curonian and Sudovian, became extinct earlier. Some theories, such as that of Jānis Endzelīns, considered that the Baltic languages form their own distinct branch of the family of Indo-European languages, but the most widely accepted opinion is the one that suggests the union of Baltic and Slavic languages into a distinct sub-family of Balto-Slavic languages amongst the Indo-European family of languages. Such an opinion was first represented by the likes of August Schleicher, and to a certain extent, Antoine Meillet. Endzelīns thought that the similarity between Baltic and Slavic was explicable through language contact while Schleicher, Meillet and others argued for a genetic kinship between the two families.