Where does “ベラルーシ” come from?

ベラルーシ (Japanese) comes from Russian Белару́сь, from Belarusian Белару́сь, from Old East Slavic Бѣла Русь — {{w|White Ruthenia}} or White Rus.

ベラルーシ (Japanese): Belarus

Definitions

Step	Language	Word	Meaning
1	Russian	Белару́сь	—
2	Belarusian	Белару́сь	—
3	Old East Slavic	Бѣла Русь	{{w\|White Ruthenia}} or White Rus

ベラルーシ — Etymology, Origin & Word History | Etymology Explorer