The standard narrative is that the 1920s policy of korenizatsiya – the promotion of “national cultures” over the Russian one across the non-Russian republics of the USSR – was reversed in favor of Russification from the mid-1930s. However, at least so far as the book publications goes, this really seems to have been more of a post-Stalin development.
Here is a graph of the number of books published in the Russian language and Belorussian language from 1924 to 1990.
Books published by language in Belarus (BSSR) from 1924-1990. In thousands; Belarusian = blue; Russian = red.
Source: Мотульский Р.С. Книгоиздание Беларуси советского периода в зеркале статистики. Беларуская думка. 2012. №1. С. 56-63. [via Alexander Khramov]
There was a similar picture with respect to Ukrainian language books, as analyzed by Ivan Ivanko for Ukrainian newspaper Pravda.com in 2010.
Books (total) published by language in Ukraine (UkSSR) from 1921-1989. In thousands; Ukrainian = black; Russian = red.
Source:Книговидання в УРСР. Скільки українською і скільки російською
In the Ukraine, we see that at the very beginning, the number of books published in Russian consistently exceeded Ukrainian language ones until the mid-1920s, five years after the introduction of Ukrainian language schooling throughout the UkSSR in 1920. We don’t have numbers for Belarus before 1924, at least on this graph, but considering that by that year the two languages were level pegging despite korenizatsiya having been introduced at about the same time as in Ukraine (i.e. several years beforehand) we can probably assume that the Russian language likewise started out in the lead there, reflecting the incipient project of building an All-Russian identity within the late Russian Empire.
In both Belarus and the Ukraine, there is only a transition to predominantly Russophone book publication by the time of the later Soviet Union. Russian language books only decidedly overtook Belorussian language ones in Belarus c.1970, and Ukrainian language ones in Ukraine c.1985. This went in line with the reversal of korenizatsiya policies, which may perhaps be dated to the 1961 CPSU program to begin a “merger of nations” into one Soviet people, which was intensified under Brezhnev. This culminated in the removal of the “soft Ukrainizer” Petro Shelest as First Secretary of the Ukrainian Communist Party in 1972 (his Belorussian counterpart Pyotr Masherov – who remained in his position from 1965-1980 – had a reputation as a Russifier).
There are several possible reasons for why the transition to Russophone dominance in Belarus preceded that in Ukraine by ~15 years. Perhaps it’s just a function of Belorussians being historically and culturally more “synced” with (Great) Russians. Perhaps political contingencies, as mentioned just above. Perhaps something to do with banal demographics and cultural weight – Ukrainians as an “audience” are five times as numerous as Belorussians, and while there are a few literary classics in the Ukrainian language, certainly the same cannot be said of Belarusian. Probably all of these reasons played some role.
Likewise, their post-Soviet trajectories were also different. Belarusian has continued fading away through to at least 2013, with the number of Belarusian language books falling to 3.9 million relative to 5.9 million in 2000 (note they were around 10 million in 1990). Despite the Crimean Crisis prompting Lukashenko into accelerating his regime’s accomodation with zmagarist elements in the cultural sphere, by 2018 that number was still essentially the same at 4.3 million versus 18.5 million Russian language books. Things have gone in the opposite direction in the Ukraine, where by 2009 there were 14.8 million Ukrainian language books published to 5.7 million Russian language ones, according to Ivanko’s figures. Ten years later, the numbers were 21.5 million and 3.0 million, respectively. This is only partially explained by the shearing away of near universally Russophone Crimea and the LDNR.
This last part is obviously more speculative, but it does suggest that Belorussians are “fixed” as Russophones for the indefinite future in a way that Ukrainians are not. I posted the following map (right, click it to see animation) tracking the evolution of Ukrainian language schooling from 1991 to 2012 in this post. Well, as of Sept 1, 2020, all of Ukraine – outside Crimea and the LDNR, of course – will go dark brown at 99%+ in line with new schooling laws. This is the logical culmination of post-Euromaidan efforts to root out the Russian language from public discourse, from the ban on Russian social network Vkontakte to removing Russian language translations from government websites.
In the Ukraine, the Russian language may well eventually become a “foreign language” in tandem with generational turnover, only regularly used by an ethnic Russian minority that will dwindle to ~10% of the population by the second half of the century. At least, such is the hope of the Ukrainizers. The Russian book market dwarfs the Ukrainian one not just in absolute terms, but relative ones (~500 million books published annually to ~25 million in Ukraine, and a similar number in Belarus). Imports could still sustain a predominantly Russophone book culture – at least, unless you ban them.