Default language

Hello, I tried to automatically recognize the user language using :
if(strstr($_SERVER['HTTP_ACCEPT_LANGUAGE'],'it')){$mlang_defaultlang="Italian";}

elseif(strstr($_SERVER['HTTP_ACCEPT_LANGUAGE'],'fr')){$mlang_defaultlang="French";}

elseif(strstr($_SERVER['HTTP_ACCEPT_LANGUAGE'],'de')){$mlang_defaultlang="German";}

else {$mlang_defaultlang="English";}
but this is not a very good approach because some have many accept_languages variables, sometimes not the prefered one in the first place.
If I put a field in the userdatabase to let know the default language, where and whow can I tell phprunner to read this field to put the default language at login ?
Thanx for every idea!

Jean