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.
Russians in Latvia
Russians were the main ethnic group in the USSR both in number and in political influence. Under the conditions of Soviet Latvia, Russian culture dominated the whole non-Latvian population of the Republic. The Russian language also formed a new group of Russian-speaking Belarusians, Ukrainians, Poles, Jews and Germans of Latvia. In the period of 1959–1979 the number of ethnic Russians in Latvia increased by 47%, but the number of non-Russians considering Russian their mother tongue increased by 78%. A highly developed infrastructure was developed in Latvia on the basis of the Russian language: a broad system of secondary and higher education, science and mass media.