The date and time format in the "Date" column in the message list is "%x(%a) %H:%M" per default (date_format in clawsrc). The format presumably changes if claws is started with (locale) environment variable LANG or LC_MESSAGES (or others?) set to something different than en_*. And then stays that way even when the environment variable changes back. (Not sure if I got that really right here.) Right now I can only do the following two things to change the date/time format: - Start claws with LANG=de_CH.UTF-8 once. After that date_format is in the right format ("%a, %d.%m.%Y %H:%M" in my case) - Edit the format in the preferences manually. One problem persists though. The abbreviations of the week days (%a) are in english instead of german. In my opinion the date format should respect locale LC_TIME and not the general language. I usually have set LANG to something different than LC_TIME. I briefly scanned the code but could not find where to make these changes so I hope someone else can point me to it.
Just set "%c" (The preferred date and time representation for the current locale.) as your date_format in Claws Mail, and message list will always use the locale's preferred format. Sorry for the late answer.