Catalan (Valencian) has no ISO 639 code assigned and the UI localization uses
the ca-XV hack where XV is of the reserved ISO 3166 user-assigned range. This
should not escape to document content therefor internally a replacement to
ca-ES is done for all locale attribution. For the UI localization to be
distinguishable under Tools->Options->LanguageSettings->UserInterface this
needed a special handling to allow Catalan (Valencian) again.