Let me see...It depends where you're starting from. I agree with Doug that it would be unlikely in such a short time. But, if you want to give it a try, it should be a full immersion course with lots of written and audio/video documents together with grammar revision and vocabulary enhancement. If that doesn't scare the hell out of you, let's try it! :)

I suppose anything is possible, but I think reaching that level in 4 weeks is very unlikely.

Moin moin, Domich, Es ist möglich, aber ein wenig unwahrscheinlich. I agree with Doug and Phil about this. However, if you have the opportunity, see if you can "live" your target language for a month. By that I mean if the language is English, only speak, read, and listen to English in this time. Study in a structured way, and then later in the day watch movies in English or call a friend and speak only English. I've never done this, but I understand it is a good method that has been useful for some. (I meant to post this as an answer rather than a comment.)

Moin moin, Domich, Es ist möglich, aber ein wenig unwahrscheinlich. I agree with Doug and Phil about this. However, if you have the opportunity, see if you can "live" your target language for a month. By that I mean if the language is English, only speak, read, and listen to English in this time. Study in a structured way, and then later in the day watch movies in English or call a friend and speak only English. I've never done this, but I understand it is a good method that has been useful for some.