Supporting multiple languages isn't just about translating text—it's about routing, SEO, user experience, and content management. This guide covers everything you need to build professional multi-language sites with Next.js 14 and next-intl. Topics include: Setting up next-intl with App Router, Language-specific routing and metadata, Managing translations with JSON files, Date, number, and currency formatting, SEO optimization for multi-language content, Language switcher implementation, Common pitfalls and how to avoid them. Based on real implementation in this portfolio site supporting English, Chinese, and Malay.