It's a modern dress, probably from the 1990s or later. Honestly, it's so ahistorical that I can't tell if it's a medieval or Renaissance costume, or if it's just a fancy outfit meant to evoke a faux-medieval vibe.

It's not really based on any specific country or era. But the velvet panel over the bust is probably meant to imitate the stereotypical underbust "wench bodice" you see at Renaissance faires, and the pattern on the fabric is a little bit like the stylized floral/pomegranate patterns on Italian brocades and velvets of the 15th and 16th centuries.