unexpected behaviour whilst fixing fdo#50118

Hi,

I'm working on a neat fix for bug fdo#50118 (Add-in functions are always shown in locale, 
regardless of global setting 'Use English function names') and I encounter an unexpected behaviour.
In /sc/source/core/tool/addincol.cxx in ScUnoAddInCollection::ReadFromAddIn() I use 
Application::GetSettings().GetUILanguageTag().getLocale() (not yet pushed, still in 
https://gerrit.libreoffice.org/#/c/6032/), which works well during start up.
But when calling Application::GetSettings().GetUILanguageTag().getLocale() again later, when the 
gobal setting 'Use English function names' has been changed, the call returns an empty locale (i.e. 
locale.Country is empty)!

Any ideas what causes this?

Winfried