I was just wondering if someone could provide documents on this if it is true, or just tell me that it never was the case. Curious about this since it is something I've always held to be true but never confirmed.
Not true, although there is a grain of truth to it. Latvia, like the other two Baltic states, restored its pre-1940 citizenship - anybody who was a citizen of independent Latvia, or the descendant of one, automatically gained citizenship in the new state. This mean that the numerous Russians (and a few Ukrainians, Belorussians, Armenians etc) who had migrated after WW2 did not automatically acquire citizenship. To gain citizenship they had to display a high level of fluency in the Latvian language which many of them found difficult to achieve (especially the elderly).
Where your father's wrong is that those who didn't obtain citizenship weren't deported - they were allowed to stay as residents of Latvia, but without the rights of citizens (e.g. they couldn't vote, couldn't run for office, weren't eligible for certain forms of state support, etc etc). Some chose to leave, some took Russian citizenship and stayed in Latvia, and some declined to take up any citizenship (which made it very difficult to deport them) and remained in Latvia in the hope of acquiring Latvian citizenship. (Latvia doesn't allow dual citizenship).
Although some Russians have left since 1991, they tend to have a higher birth rate than Latvians, and their presence is still very much in evidence - Riga is almost 50% Russian, and in Daugavpils, Latvia's second city, they form a majority. Civil servants in these areas are generally expected to know at least some Russian and many services (e.g. education) can be provided exclusively in Russian.
The situation is parallel in Estonia, although the number of Russians in Estonia is smaller. In Lithuania Russians were granted citizenship, possibly because they made up a smaller % of the population (about 14%, as opposed to about 28% in Latvia and 30% in Estonia).
Source: A History of Latvia, Alfred Bilmanis
Language policy was definitely implemented; Latvia was inspired by the Charter of the French Language passed in Quebec, and used that as a basis for creating a similar language policy trying to curb the increasing dominance of Russian and retain Latvian as the primary language of the country.
I can't speak to the claims about deportation, but if you are interested in more information about the language laws there is a great article that compares Quebec and Latvia.
This is the citation:
Schmid, C., Zepa, B. & Snipe, A. (2004). Language policy and ethnic tensions in Quebec and Latvia. International Journal of Comparative Sociology, 45(3-4), 231-252.