score:2
Here is what New World Encyclopedia states, shortly after the Truce of Deuolino (1619):
Livonians here mean inhabitants of Polish-Lithuanian Livonia which included Latvians, Estonians, Baltic Germans and Livs.
Upvote:5
It was very diverse. It contained Poles (who spoke Polish), ancestors of modern Ukrainians and Belarussians (who spoke in various dialects, which later became Ukrainian and Belarussian languages), they were called Ruthenians at that time, Lithuanians, Germans, Jews (speaking Yiddish and using Hebrew for religious purposes), Tatars (with their own languages), Armenians, Karaites and several other ethnic groups, smaller in numbers. I think I listed all largest groups.
The (English) Wikipedia article has a list of languages, and marks which of them were officially recognized. In addition to those I listed, Latin was an officially recognized language. For the sources, the mentioned Wikipedia article contains a lot of them, and I can add the books of Timothy Snyder.