I am usig CMS 11 version. However, edit mode sets culture to en-us even when my site is in en-gb. So, when I open both in same browser, language gets set to en-us and en-gb for edit mode and site respectively. I found similar issue in the following post but there is no solutions.
I have webconfig setting as below.
<globalization culture="en-US" uiCulture="en" requestEncoding="utf-8" responseEncoding="utf-8" resourceProviderFactoryType="EPiServer.Framework.Localization.LocalizationServiceResourceProviderFactory, EPiServer.Framework.AspNet" />
Hey Muller,Sorry for the delayed response, I just got back from Christmas holidays, happy new year!
Check out the Globalization section of the developer documentation; https://world.episerver.com/documentation/developer-guides/CMS/globalization/
The answer is in the bullet points in System language and User Interface language sections.
Let us know how you go.