The language negotiation is extendable, you just need to implement hook_language_negotiation_info(). In there, you can do whatever you want, like always default to swedish for now. It also looks like you can limit to what languages you can switch to, I am not sure how that exactly works, though.

Not sure what to do once you add more languages, but you could for example call other negotiation callbacks in yours and fallback to swedish if it not one of the languages you want displayed.

You’re probably here because you’ve the delightful task of creating a multilingual Drupal 7 installation.
Things have been going OK, you downloaded and installed i18n, switched some translation modules on and happily started inputting content and adding translations.  You figured it was time to created some front pages, of course a separate one for each language, otherwise what’s the point. You figure it’s as easy as creating and translating other nodes, so you do that, set the default front page, take a look, switch the language and…. it doesn’t work!