The Ukrainian language is after Russian the most widely spoken language in the former Soviet Union. As many as 42 million people speak Ukrainian, at least according to Wikipedia, but only 31 million of these live in a Ukraine that's home to a bit over 46 million people. Ukrainian census data suggest that 31.9 million ethnic Ukrainians out of 37.5 million speak Ukrainian, with a bit over two-thirds of the Ukrainian population speaking Ukraine. The linguistic situation is more complicated than that, with many ethnic Ukrainians who mostly do not use Ukrainian in day-to-day life identifying Ukrainian as their mother tongue based on ethnic identity. The Ukrainian population may well be divided equally between speakers of Ukrainian and Russian, with Ukrainian predominating in western and central Ukraine and Russian predominated in southern and especially eastern Ukraine. There are signs of a shift towards Ukrainian, with Ukrainian becoming a trendy language a mostly Russophone Kyiv and education and government services being delivered in the Ukrainian language, but it's clear that Russian is in Ukraine to stay.
The same is doubly true of Kazakhstan, as Joanna Lillis at Eurasianet describes. Before the dissolution of the Soviet Union, Russians and Russophones actually constituted the majority population of Kazakhstan. Though this majority has been whittled away thanks to massive Russophone (and German) emigration and a substantially higher Kazakh birthrate, the linguistic legacies of this Russian domination remain.
The problem is exacerbated by the contentious language issue in Kazakhstan: a recent poll showed that only about a third of inhabitants speak fluent Kazakh, while 16.3 percent do not speak the titular language at all. The poll was conducted by the Alternativa Center for Topical Research with the Open Society regional research institute (the organization is not connected to the New York-based Open Society Institute, under whose auspices EurasiaNet operates). Out of the poll’s 1,200 respondents, 36 percent characterized their Kazakh-language skills as fluent, while an additional 20 percent claimed a sufficient knowledge of the language. In stark contrast, 90.4 percent of respondents qualified their Russian language skills as either fluent or sufficient, fuelling arguments by ethnic Kazakh nationalists that not enough is being done to promote the spread of the titular language. The polling data was released in November.
This has proved problematic in the wake of the Soviet-era policy of Russification which took strong root in Kazakhstan, where ethnic Kazakhs were in a minority at independence in 1991. "[Russification] had a catastrophic effect on the influence of Kazakh language and culture," Nazarbayev told the APK, which conducts most of its business in Russian. His call for it to be at the center of efforts to promote Kazakh language learning struck some commentators as illogical. "Without having a scientific and linguistic basis, without even speaking Kazakh, how is the Assembly going to develop the state language [Kazakh]?" the Taszhargan weekly asked rhetorically.
Finally, the Belarusian language, like Ukrainian an East Slavic language, may be on the verge of language death. Belarusian "is declared as a "language spoken at home" by about 3,686,000 people (36.7% of the population) as of 1999. By less strict criteria, about 6,984,000 (85.6%) of Belarusians declare it their "mother tongue"." The Russian language is by all accounts firmly implanted in Belarus, as it is the predominant language of Belarusian cities, Russians form the country's largest ethnic minority, and the government under Lukashenko has done very little to promote the use of Belarusian and has instead allowed it to be exposed directly to a much stronger Russian language. Belarus is likely to survive as a nation-state, but it's also likely to be a society like (say) Ireland where the native language has been firmly minoritized.