how to change language of format-date-string

[Rasmus]

Hi,

I would like to change the language that format-date-string assumes, as my
OS is not in English for leaning purposes.  I tried to issue
(set-language-environment "English"), but this does not seem to have an
effect.

I tried to grok the code it editfns.c, but I'm not really sure what is
going on...

I'd appreciate any hints.

—Rasmus

-- 
. . . The proofs are technical in nature and provides no real understanding