"Belarusian" (derived from contemporary English name for Belarus)
"Belorussian" (based on transliteration of Russian)
"Byelorussian" (transliteration of Russian in pre-1918 orthography)
"White Russian" (literally translation)
As far as know everyone uses "Belarusian" here.
Since Englishmen call Czechs in Polish, I don't see a problem in calling Balarusians in Russian.
It should be as \\\"Belorusiani\\\" call their own country. Not as Russians or English do that.
Any language has the right to call any nation as the speakers of the language like. Or do you think we should call the US Junajtid Stejts ov Amerika, Japan Nipon, Southern Korea Anguk, China Czungkuo etc.?
Of course, Slovianski-P has Belorusija, beloruski and belorus/belorusi.
Wikipedia is in large scale a tool of manipulation of fools and naiive ones, as only too many biased maniacs, and somtime even outright fools, can redact it only too easy at too many occasions. It is full of rubbish and biased reject designed to serve no one looking for reliable information but rather ignorants.
Sometime, but only if you are informed previously of some topic from other, more reliable sources you can find some interesting additional facts, but I really recommend never trust it as a reliable information source. It can be of some use, but rather as only source of interesting sometime, but invalid until double checked information.