The Russian war in Ukraine increased the use of the Ukrainian language on social media. Researchers analyzed 4.45 million geo-tagged tweets from 62,712 users between January 2020 and October 2022 to examine language choice and tweeting activity. They found a steady shift from Russian to Ukrainian language use, which accelerated significantly after the Russian invasion in February 2022. More than half of Russian-tweeting users switched to Ukrainian. The study attributes this shift to users' conscious choice to identify more with Ukrainian culture and identity. Social media plays a critical role in political shifts and crises, and can be used for crisis informatics, such as disaster monitoring. The study also found that users' language choice online reflects their self-presentation and identity. The analysis showed that users' language use changed due to both sample effects (user turnover) and behavioral changes. The study used statistical models to disentangle these effects and found that users' language use shifted significantly after the war. The results show that users who switched from Russian to Ukrainian did so in response to the war, with many making a hard switch. The study also found that users who switched to Ukrainian had more followers, higher tweet and like frequencies, and published more Ukrainian geo-tagged tweets. The study used multilingual topic modelling to analyze the content of tweets, finding that users who switched to Ukrainian tweeted more about the war. The study highlights the role of social media in shaping language use and identity during times of conflict.The Russian war in Ukraine increased the use of the Ukrainian language on social media. Researchers analyzed 4.45 million geo-tagged tweets from 62,712 users between January 2020 and October 2022 to examine language choice and tweeting activity. They found a steady shift from Russian to Ukrainian language use, which accelerated significantly after the Russian invasion in February 2022. More than half of Russian-tweeting users switched to Ukrainian. The study attributes this shift to users' conscious choice to identify more with Ukrainian culture and identity. Social media plays a critical role in political shifts and crises, and can be used for crisis informatics, such as disaster monitoring. The study also found that users' language choice online reflects their self-presentation and identity. The analysis showed that users' language use changed due to both sample effects (user turnover) and behavioral changes. The study used statistical models to disentangle these effects and found that users' language use shifted significantly after the war. The results show that users who switched from Russian to Ukrainian did so in response to the war, with many making a hard switch. The study also found that users who switched to Ukrainian had more followers, higher tweet and like frequencies, and published more Ukrainian geo-tagged tweets. The study used multilingual topic modelling to analyze the content of tweets, finding that users who switched to Ukrainian tweeted more about the war. The study highlights the role of social media in shaping language use and identity during times of conflict.