Solange comes from the Latin sollemnia, meaning "solemn ceremony" or "sacred rite." Saint Solange (died 880 CE) is a French martyr; the church of Sainte-Solange near Bourges bears her name.
Solange 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 Solange reduce to 1, The Leader. This is a traditional interpretive system, not a factual claim about the name.