Our application supports language/locale switching on the fly when users log on or off. As part of this we set the FrameworkElement.Language property on the MainWindow, which is then inherited throughtout the visual tree.
We found a problem were the Language on all our tool windows was not being inherited but was always "en-us". Further investigation showed this was because we add the tool windows using the Prism region manager with a DockSiteRegionAdapter - a tool window added directly to the dock site in XAML behaves OK.
I've sent a sample demonstrating this to the support address