Hi @Rada Matěj, I reproduced your issue finally in my side with your resource file and I also test if within blazor server app, and I found the issue only occurred in blazor wsam project, but in server app, it worked well.
This shall be the expected behavior of blazor wsam as CultureInfo.GetCultureInfo is defined as retrieving a cached, read-only instance of a culture, which only work in the server side.
When we want to get different results based on different culture in blazor wsam app, we need to follow this section. I had a test in my side which worked well. In the meantime, it requires to reload the application by using Navigation.NavigateTo(Navigation.Uri, forceLoad: true);
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Best regards,
Tiny