For future reference, I updated 2 sites at about the same time. They were always in Turkish but switched to English with the theme update.
The first site switched back to Turkish after about 6 hours and the second site after around 18 hours. So there is definitely a delay. I hope the same is not true for future updates – I have to keep an eye on the site and then clear the site cache (created by the cache plugin) after the change.