Since i am looking for internship and my country is not in EU … ( but i can travel for 90 days anywhere expect for UK ) - how much problems do emlpoyees make about this? I am willing to go in internship but i need work permit/visa.
Personally I would target larger companies with dedicated HR departments. They are much better equipped and experienced with that kind of administrative work. Downside is that a majority of the will probably be inhouse-positions, rather than design consultancies.
following bngi´s advice, your best options is probably to look at the carreer sites of big companies that you want to work for. From your portfolio it looks more like you are a transportation designer, so try to reach out to BMW, FIAT, SKODA or others in that area. If you also want to go for other companies, google them and see if you can either find an open posted position, or at least some contact mail that you can send your application to.
Point being is, that in your case it is best to ask big multi-million dollar companies, that are used to handling visas.
But you should ask your government, what exactly the situation is with working in the EU. As long as there isn´t any other designer from serbia on the board reading your question, none of us can help you with that.
Smaller places are not going to know what the process would be like and that could be off-putting. so at least you should be able to provide the information of what has to happen for you to be able to work there.