[eluser]xwero[/eluser]
Most of the time multi language sites have the same content and only the text changes based on which language the user chooses so there is no need to change the base url depending on the chosen because the language segment in the url is virtual and not physical.
If the separation is physical, for instance a different subdomain, you can create different applications based on one CI/site core. That way each app has its own base_url setting.
To summarize the settings in the config.php file should be application wide and should only change if there is no other solution.
