[TYPO3] set language variable from TS

[Sebastian Fuchs]

Hello,

I have a multilinguage website, following the One-Tree concept, but with 
different trees for different countrys.
So wright now a user selects a country-tree and browses in there. this 
results in the &L-Variable becomes set to e.g. 5 (russian language).

when he comes back to the country selection site i would like to unset 
the query string &L variable.
because otherwise if he chooses a different country (where no russian 
site are in) he gets a an error message (no page available in this 
language).

i know i can set the config.sys_language_uid to what ever i like, but i 
want to set the &L variable to the correct value.
does anybody know a typo3 way of doing this? or do i have to use a hard 
redirct (with header:location )?

thanks a lot,
sebastian