Henning,
That's a interesting question...
From the options in Windows Live Writer, it's not possible [right now ] to assign a language to a specific blog, but I would offer this suggestion/workaround; research AutoHotKey.
www.autohotkey.com
You say you've to switch between languages; I understand, but if a macro could do this for you [...] it wouldn't be so bad... right?
I offer you this...
::^g ;CTRL-g for German Blog
;; Switch to German Blog
send, {altdown}b{altup}
send, {down 5} ; to the blog
sleep, 500 ;pause
;; Switch the language
send, {altdown}t{altup}
send, o ;options
send, {down 5} ; to the language options
send, {space}{tab} ; language selection box
send, {home} ;top of the list
send, {down 4} ;select language you want
;; on my machine this selects United States English, but change the number to whatever you need.
send, {enter} ; close options.
return
You could improve this, but this shows roughly how to select a blog and change the language with a single key stroke.
I hope this helps...
Until next time,
LEHenryJr
LEHSYS.com
If you this answers your question, please 'propose as answer' for other users.