Blanka is from the Czech / Polish / Hungarian Blanka — Central European rendition of Blanche — from the Old French blanc (white). Blanka is one of the Czech + Hungarian + Polish feminine names. Blanche of Valois (Blanka z Valois, 1316-1348) was the first wife of Holy Roman Emperor Charles IV + Queen of Bohemia — central to medieval Czech royal heritage.
Blanka does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Blanka reduce to 5, The Seeker. This is a traditional interpretive system, not a factual claim about the name.