The current localization is automatically detected by looking at Thread.CurrentThread.CurrentUICulture.
This only happens when the localization is accessed for the first time.
Runtime changes to Thread.CurrentThread.CurrentUICulture are not monitored.
All currently supported localizations live in the namespace Fluent.Localization.Languages.
If you want to ignore the threads current ui culture you can set the current localization by calling RibbonLocalization.Current.Localization = new German() or by calling RibbonLocalization.Current.Culture = new System.Globalization.CultureInfo("de").