Currently weekdays are abbreviated with three letters. That is not correct. According to chapter 5.3.3 in https://www.bk.admin.ch/dokumentation/sprachen/04915/05016/index.html?lang=de&download=NHzLpZeg7t,lnp6I0NTU042l2Z6ln1acy4Zn4Z2qZpnO2Yuq2Z6gpJCHe393gWym162epYbg2c_JjKbNoKSn6A-- weekdays have to be abbreviated with two letters and without a dot, e.g. "Mo" for Montag (Monday), "Di" for Dienstag (Tuesday) and so on.
we discussed this a bit on the lists already: https://sourceware.org/ml/libc-alpha/2016-02/msg00144.html
Fixed by this commit: commit 2a124c616384f140a21ee675b3e6799f8e0e7592 Author: Mike FABIAN <mfabian@redhat.com> Date: Mon Aug 14 17:12:37 2017 +0200 Use two letter abbreviations in abday in all German locales. [BZ #20482] * locales/de_AT (LC_TIME): Use 2 letter abbreviations in abday. * locales/de_BE (LC_TIME): Use 2 letter abbreviations in abday. * locales/de_CH (LC_TIME): Use 2 letter abbreviations in abday. * locales/de_DE (LC_TIME): Use readable ASCII in abday. * locales/de_IT (LC_TIME): Use readable ASCII in abday. * locales/de_LU (LC_TIME): Use 2 letter abbreviations in abday.
*** Bug 15357 has been marked as a duplicate of this bug. ***