Comment # 19 on bug 905623 from Christian Bachmaier

$ su
passwd:
# locale
LANG=POSIX
LC_CTYPE=de_DE.UTF-8
LC_NUMERIC="POSIX"
LC_TIME="POSIX"
LC_COLLATE="POSIX"
LC_MONETARY="POSIX"
LC_MESSAGES="POSIX"
LC_PAPER="POSIX"
LC_NAME="POSIX"
LC_ADDRESS="POSIX"
LC_TELEPHONE="POSIX"
LC_MEASUREMENT="POSIX"
LC_IDENTIFICATION="POSIX"
LC_ALL=
# cat /etc/fonts/local.conf
<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<!-- /etc/fonts/local.conf file for local customizations -->
<fontconfig>
  <!-- prevent yast2 to use Arial Black instead of Arial -->
  <match target="font">
    <test qual="any" name="family">
      <string>Arial Black</string>
    </test>
    <edit name="family" mode="assign_replace">
      <string>Arial Black</string>
      <!--string>Arial</string-->
    </edit>
  </match>
</fontconfig>
# yast2
# fc-match Arial:style=black
ariblk.ttf: "Arial Black" "Standard"
# fc-match Arial:weight=210
ariblk.ttf: "Arial Black" "Black"

> Still no luck with yast dialog in german locale?

sorry, no.