In the beginning, modern dance was revolutionary. But these days, the form can be fraught with conventions, so much that it can lose that initial sense of freedom and possibility. In the West, that is. In developing countries, where dance is still frequently dominated by tradition, modern dance offers an escape hatch for movers looking to express themselves more fully. That’s what makes a show like “Voices of Strength,” which spotlights contemporary African dancers, so exciting. Featuring five female choreographers who hail from Morocco to Mozambique, the two-night “mini-festival” gives viewers a glimpse of experiences radically different from their own—ones where individuality and expressiveness aren’t guaranteed.