If unspecified with the request, the product (upon determining the country for the verification) identifies all the languages spoken in the region and picks up the most appropriate language available. In this case, Polish is one of the most widely spoken languages in Ukraine, next only to Ukrainian. Because we do not have Ukrainian Text-To-Speech, the next best match available is Polish and we fall back to that. Unfortunately, the best way to handle this would be to specify a locale with your request.