I've been going over election results in Ukraine since the end of the last century, and they are characterised by stability in the east (support for the Communist Party, then to the pro-Russian parties), and extreme volatility in the rest of the country. The Ukrainian national-fascists (Svoboda) peaked at 10% in 2012, and participated in government during 2014, then disappeared into insignificance; the Orangists also rose and fell. The Macronist Zelenskiy appeared out of nowhere and gained an absolute majority.

In 2014, the pro-Russian parties controlled both the presidency and the Parliament. It was they who were negotiating with the European Union and had agreed to sign the association agreement, before suddenly balking and signing a deal with Russia.

It is quite surprising that they should have negotiated such a bad deal with the EU (we agree on the fact that it was a lousy deal); my retrospective suspicion that they did not negotiate in good faith, but had prepared the alternative deal with Putin.

It does not surprise me that the Russians did not expect Maidan. As the events of this year make clear, their intelligence is not as good as they think.

Why would the people of Donbas accept the new government that replaced the one they voted in overwhelmingly?

Why would anyone accept an election they didn't win? In fact, (setting aside the parts that couldn't vote : Crimea and the occupied Donbas), the pro-Russians were disenfranchised by the voluntary withdrawal of the Party of the Regions from the parliamentary elections of 2014 : ostensibly because they claimed that the elections lacked legitimacy because the people in the seceding regions couldn't vote! A bit circular.

As for the status of the Russian language, I can't find any political parties which called for eliminating Russian from Ukraine. In fact, Ukrainian is the only official language since the 1996 constitution (which explicitly protects the use of Russian and other national minority languages). The language issue in the context of 2014 appears to be something of a beat-up; but clearly, over the last eight years, with a low-level, then high-level war with Russia, the position of  a lot of people has no doubt evolved.

I brought up the American civil war because you posed the question of moral equivalence between the Maidan revolution and the Donbas secession. The US civil war was the first example of secession that came to mind. But the analogy is quite weak; the US case was endogenous, whereas the Donbas rebellion was always about transferring the region from Ukraine to Russia (or perhaps you disagree?)

_{It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II}