Hi,

What is the culture set for the site in Site Manager -> Sites -> edit your site -> Default visitor culture field?
Please note that log out and in again may be necessary and/pr the application restart as well. Moreover, if some user has set his/her browser to use other culture, this will also take effect.

When editing the site, there is also a field "Default content culture" - you can also try to change this culture and please check the box in the new opened window, so all the documents are changed to this new culture.

Best Regards,
Juraj Ondrus