The relevant part seems to be
The reason why you don't get the crash with the official viewer, is because the display settings are ok and the viewer does not pop up the dialog (try deleting the ~/.secondlife/user_settings/settings.xml file and start again the official viewer to confirm this), while the Cool SL Viewer uses settings_coolslviewer_wl.xml and the one you got on your system is either missing or the one for v1.21.6.0, which triggers the alert, and then the crash.
This bug seems related to a locale issue and was already reported many times on the JIRA, such as:
VWR-11898.
It is probably a problem with the German alert.xml file and the locale used by the viewer while reading it.
The work around is to include the following line, at the start of the "secondlife" script:
export LC_ALL=C
Try it...