Not exactly sure since when (but most likely not throughout the full Leap 42
lifecycle) my language settings are somehow mixed up in at least two
applications.

1. Gtk3 file dialog
Please see attached screenshot to see the mix between german and english
language.

2. Libreoffice
Libreoffice Calc requires me to enter formulas in english while the UI is in
german.

I'm running under Xfce on Leap 42.3 with all updates but so far I only have
seen Gtk applications affected.

wolfi@Hygiea:~> locale
LANG=de_DE.UTF-8
LC_CTYPE="de_DE.UTF-8"
LC_NUMERIC="de_DE.UTF-8"
LC_TIME="de_DE.UTF-8"
LC_COLLATE="de_DE.UTF-8"
LC_MONETARY="de_DE.UTF-8"
LC_MESSAGES="de_DE.UTF-8"
LC_PAPER="de_DE.UTF-8"
LC_NAME="de_DE.UTF-8"
LC_ADDRESS="de_DE.UTF-8"
LC_TELEPHONE="de_DE.UTF-8"
LC_MEASUREMENT="de_DE.UTF-8"
LC_IDENTIFICATION="de_DE.UTF-8"
LC_ALL=