Confusing choices of region and language
The web site has independent and separate settings for region/country and for language. This makes it very flexible but in a way that is unusual. The choices are not labeled and I think it will be confusing for most users. They will find the setting for region in the top right corner. A placement often used for settings of language. They will probably expect that setting to control language. I did.
When it did not change the language I thought it was a bug, until I scrolled all the way down to the bottom of the page. Then I realized that there where separate settings for region/country and language.
Have both settings at the top right position. Label them both to make it clear.
You could still have both settings also at the bottom right, but with added labels.