You could have some Arabs wandering around and settling somewhere in Eastern Europe. Of course, the catch is that eventually it won't be "ethnic Arab" per se, but ethnic *[insert-demonym-for-ficticious-Eastern-European-country-here]. However, the new language, whilst absorbing words from all over the region and probably written with some form (say a mixed OTL Czech/Polish/Hungarian/Romanian) as well as probably undergoing major changes in phonology, would definitely use Arabic grammar.