I would become fluent in Mandarin Chinese. Being fluent in Mandarin would open up opportunities to connect with over 1 billion Chinese speakers worldwide. I would use this skill to build cultural bridges, do business in China, immerse myself in the richness of Chinese arts and history, read classical Chinese literature in its original form, and gain insights into a truly ancient and fascinating civilization. The potential benefits of learning Mandarin in today's global world are hugely impactful.