The importance of language in the escalating crisis in Ukraine came to the fore when Russian President Vladimir Putin justified deploying troops in Crimea by saying Moscow needed to protect Russian speakers there.

Traditionally, the west of the country as well as the capital Kiev has been Ukrainian-speaking, while the east and south — closer to Russia and including the explosive peninsula of Crimea — speak Russian.

But most Ukrainians are bilingual and switch naturally between languages depending on the situation.

Now after the incursion of Russian troops in Crimea and with a pro-European government in Kiev, the sound of words has never been more political.

“In politics, the use of language is a signal: ‘with us or against us’,” Ukrainian sociologist Iryna Bekeshkina told AFP.

After Russia’s parliament gave Mr. Putin the green light to send troops into Ukraine, many Kiev residents have started speaking only Ukrainian as a sign of protest against the Kremlin’s actions.

Members of ousted president Viktor Yanukovych’s Regions Party usually speak Russian, while ex-prime minister and icon of the former opposition Yulia Tymoshenko, a Russophone, refuses to speak it even in interviews to Russian journalists.

Russian and Ukrainian are both eastern Slavic languages. But despite similarities in grammar and vocabulary and almost identical alphabets, they differ sharply in many ways and are not mutually intelligible.

Many Ukrainian-speakers consider the language to be closer to Polish than Russian. While Russian was the official language of the Soviet Union, Ukrainian was also taught in schools here, so that every Ukrainian can read and write in that language even if they do not speak it at home.

Studies show just one percent of the population does not understand Ukrainian, while 30 percent do not speak it fluently, and the proportions are similar for Russian, said Bekeshkina.

Remarkably, however, a majority of people in many eastern and southern regions gave Ukrainian as their mother tongue in the last census from 2001.