Latgalian language
Latgalian is spoken in Latgale, the eastern part of Latvia. It is debated whether it is a separate language or a distinct dialect of Latvian. Nevertheless, its standardized form is recognized and protected as a "historical variety of the Latvian language" "(vēsturisks latviešu valodas paveids)" by Latvian law. The 2011 Latvian census established that 8.8% of Latvia's inhabitants, or 164,500 people, speak Latgalian daily. 97,600 of them live in Latgale, 29,400 in Riga and 14,400 in the Riga region.
Latvian language
According to some glottochronological speculations, the Eastern Baltic languages split from Western Baltic (or, perhaps, from the hypothetical proto-Baltic language) between 400 and 600. The differentiation between Lithuanian and Latvian started after 800, with a long period of being one language but different dialects. At a minimum, transitional dialects existed until the 14th century or 15th century, and perhaps as late as the 17th century.