How to Implement Internationalization (i18n) in Spring Boot - Using MessageSource and LocaleResolver
A practical guide to implementing internationalization (i18n) in Spring Boot REST APIs. Covers language switching via the Accept-Language header, locale fallback with messages.properties, configuring MessageSource and AcceptHeaderLocaleResolver, localizing @Valid validation error messages, and returning multilingual error responses with @RestControllerAdvice, all in one end-to-end walkthrough.