Should I avoid „družstevní byt“? Do I even have possibility to take mortgage ?

 The flat - "druzstevni byt" means that a flat belongs to a cooperative of shared flat users. No one owns a flat, they are only a user with the right to live there until someone else buys into the cooperative. Basically, you don't buy property, you buy only the right to share a flat in the cooperative. This type of property is not suitable for you, especially as you are a foreigner. By law, most banks, cannot hold this type of flat pledged. So it would be necessary to offer the bank another private property as collateral. I think this might not be suitable for you. Some banks accept this type of flat as a pledge, but the board of the cooperative must agree with your "hypoteka - mortgage" and the cooperative must have official plans to convert the property from a cooperative type of property to a private property. However the flat has to be converted into a private property within one year after signing the mortgage with the bank. It must be absolutely clear in the Statute of the Cooperative. This document, promising the fact that indeed they are changing the property rights to private, must be admitted only in written form. Otherwise you should have a pre-mortgage loan, which is more expensive than a normal mortgage and full of many unfavorable conditions. 

"Nesplacená anuita - outstanding annuity" is the rest of the debt owed by the current owner to the cooperative, which needs to be paid back to the cooperative (the legal owner of the building and flat also) before the flat is transferred into your name.