Problem

Error messages are hardcoded throughout the codebase.

Examples

throw new NotFoundException("$"Group with ID '{command.Id}' not found."); throw new CustomException("Toggle status failed", errors); await context.Response.WriteAsync("Endpoint not found.");

Files affected

• All handlers with validation
• Exception messages
• Response messages

Suggested approach

1. Create Resources/ErrorMessages.resx
2. Use IStringLocalizer<T> for messages
3. Create constants for error codes

Impact

• Cannot localize application
• Inconsistent error messages