-={ söndag, 04 oktober 2015, 08:06:44 +0200 }=-

Hey Holger!

 HG> Well it doesn't help my efforts, since I don't have the source
 HG> code.

Understood.  That is why I started writing my own over the years.

 HG> countries I know use the "old" format of dd/mm/yyyy

I haven't seen it that much.  My direct uplink uses "2015/10/03 21:59:19 -8:00"
which is "%Y/%m/%d %T %z" and is convertable as shown in the below example;

:r !date --rfc-3339=seconds --date="2015/10/03 21:59:19 -8:00"

2015-10-04 05:59:19+00:00

Testing the old format where dd/mm/yyyy becomes 03/10/2015 yields;

:r !date --rfc-3339=seconds --date="03/10/2015 21:59:19 -8:00"

2015-03-11 05:59:19+00:00

Which isn't the same thing.  Not sure what locale setting would be needed to
get the correct result.  According to
https://en.wikipedia.org/wiki/Date_format_by_country Sweden's format is
yyyy-mm-dd which is the same as %F which is what my uplink uses except with /
seperators instead of - seperators.  For the record your msg header datetime
with a +0200 timezone tacked on translates to;

:r !date --rfc-3339=seconds --date="03 Oct 15  10:28:00 +0200"

2015-10-03 08:28:00+00:00

which works out perfectly from this angle.

 HG> Even Australia seems to stay with the old format.

I see it listed as dd.mm.yyyy and using that format and en_AU gives me an error
even if I set LC_TIME=en_AU which is the locale setting for Australia.  It
could be an issue with modern C libs.  I'll have to check it out.  Thanks for
the heads up.

Life is good,
Maurice

... Don't cry for me I have vi.
--- GNU bash, version 4.3.42(1)-release (x86_64-unknown-linux-gnu)