Updated : 25/04/2017
NO - You can only file for divorce in the Czech Republic if you move back and live there for at least six months (if you are Czech) or one year (if you are not). As long as you remain in Germany, you can file for divorce there, as the country where you last both lived together.
NO - It will not necessarily be the law of the country where the courts handling the case are located.
Some EU countries have agreed on rules for determining which country's laws apply – Austria, Belgium, Bulgaria, France, Germany, Hungary, Italy, Latvia, Lithuania, Luxembourg, Malta, Portugal, Romania, Slovenia and Spain.
But if countries other than these are involved, it can be very hard to predict which laws will apply. Given the uncertainty this can create, with national laws often differing greatly, it is best to consult a specialised lawyer about where to file.
NO - A divorce (or legal separation or annulment) granted in any EU country (here, Sweden) will automatically be recognised in any other (here, Poland), without any special procedure.
You can, however, get your Polish documents certifying your marital status updated on the basis of the Swedish judgment once it is final ("final" means appeals against it are no longer possible)