Putin's claim "to protect Russians and the Russian language in Ukraine" is not new. It was first uttered before he inflicted in 2014 the war in the Donbas. His claim can be challenge by looking at the following:
Historical continuity is a term used to determine whether a chronological continuation has never been changed in order to conclude if something or someone is not native but has a primordial nativity, meaning being there since a very beginning.
No single country in Europe, the Americas and Asia can claim that its inhabitants are primordial native. Just look at the map below.
And so should anyone view how a tiny region sprouted into a country as it is today. Russia for example that had to be exist after centuries of expansion from the roots were once Moscow began to exist. The video below shows very clear that Russia and the Soviet Union had centuries to wait for that moment. Putin doesn't know the birth of his own country!
Now have a look at the map below and see the presence of Russian speaking people in Ukraine at the time of the Soviet Union. You can see that the presence was minor.
In 1918 there was the Ukrainian Soviet Republic, which became one of the founding states of The Union of Soviet Socialist Republics in December 1922. There was no Russia, and there was no Ukraine at that time. Ukraine was then called Ukrainian Soviet Socialist Republic.
Those living in the Ukrainian Soviet Socialist Republic and who spoke the Russian language supposed to be named Ukrainian Soviets, not Russians. Just compare it with other Soviet members. None of them were called Russians but named after the member state for example Chechen, Kazakhs, Georgians, etc.
Those in the Donbas, who call themselves "Russian" is by self-declared naming, not by primordial nativity.