Quote Originally Posted by zxc View Post
Sorry, I wasn't quite clear. I meant to ask whether it would be easier for a person who natively speaks English, but knows Russian, to learn Ukrainian, or would it be easier for him to learn Belarusian? I'm trying to decide which one to start with.
if so, echoing what it-ogo said in my opinion Belarusian is a tad closer to Russian lexically but Ukrainian is closer sonically

i'd start with Ukrainian, cause if you plan to continue on to Belarusian after that, knowing Ukrainian will help you tremendously on the lexical front

Belarusian is somewhere in the middle between the two other languages (totally subjective), so knowing the extremes you'll be able to crossbreed them