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
During the Soviet occupation (1940–1991), the policy of Russification greatly affected the Latvian language. Throughout this period, many Latvians and Latvia’s other ethnicities faced deportation and persecution. A massive immigration from the Soviet republics of Russia, Ukraine, Belarus and others followed, largely as a result of Stalin's plan to integrate Latvia and the other Baltic republics into the Soviet Union by means of Russian colonization. As a result, the proportion of the ethnic Latvian population within the total population was reduced from 80% in 1935 to 52% in 1989. In Soviet Latvia, most of the immigrants who settled in the country did not learn Latvian. Today, Latvian is the mother tongue of more than 60% of the country's population.