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.
Russian language in Latvia
According to the 1897 Imperial Russian Census, there were 25,630 (3.8%) speakers of "Great Russian" in the Governorate of Courland and 68,124 (5.2%) speakers of "Great Russian" in the Governorate of Livonia, making Russian-speakers the 4th largest linguistic group in each of the governorates.