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.
Pitch-accent language
Two languages of the Baltic branch of the Indo-European family survive today, namely Lithuanian and Latvian. (Another Baltic language, Old Prussian, died out in the 18th century.) Both languages have a tonal accent that is believed to derive from the ancestral Proto-Indo-European language.
Baltic tones are often classified as either "acute" or "circumflex." However, these labels indicate a diachronic correspondence rather than a phonetic one. For example, the "acute" accent is falling in Lithuanian but a high level tone in Latvian and is presumed to have been rising in Old Prussian and Classical Greek. The "circumflex" is rising in Lithuanian but falling in Latvian, Prussian and Classical Greek.