feat: Inconsistent i18n Message Resolution in Spring Cloud Environment

[dennis9486]

In a Spring Cloud microservices environment, we are experiencing inconsistent internationalization (i18n) message resolution across services and request contexts.

Specifically:

• MessageSource.getMessage(...) works correctly in:
  • Controllers
  • Standard HTTP request threads
• But fails or returns default messages in:
  • Async tasks (@Async)
  • Reactive contexts (WebFlux)
  • Feign client fallback / error decoder
  • Global exception handlers
  • Scheduled jobs

The resolved locale is sometimes:

• null
• Always Locale.getDefault()
• Or different from the request's Accept-Language header

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Expected Behavior

• Locale should be resolved consistently based on:
  • Accept-Language header (for HTTP requests)
  • Explicitly set LocaleContext
• i18n messages should work uniformly in:
  • Controllers
  • Exception handlers
  • Async tasks
  • Reactive pipelines
  • Feign-related components

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