title_body: Is there any evidence that learning a zonal Slavic conlang can help conversing with native speakers of Slavic languages
upvoted_answer: Yes, they show. Slovio is not a zonal conlang, it is supposed to be a kind of Slavic Esperanto. It took place 20 years ago, but nowadays noone wants to use it.
  
  Nevertheless, Interslavic is comprehensible for all Slavic people. Speaker of Interslavic went abroad to different Slavic countries and expressed their idea using Interslavic instead of native languages or English. And it worked. People understand the meaning, though the language can sound strange or event funny to them. And if it does, Interslavic is a viable project and succeeds in its challenge.