To prevent a caption from being translated in an extension for Microsoft Dynamics 365 Business Central, you should add the Locked = true parameter to the Caption (C). This parameter explicitly marks the caption as locked for translation, ensuring that it remains unchanged across different language versions of the extension. This approach is useful for specific terms, brand names, or other elements within the application that should remain consistent regardless of the user's language settings. Unlike the other options, which involve manual manipulation of the translation file or properties, setting Locked = true directly in the AL code provides a clear, maintainable, and error-proof method to exclude specific captions from the translation process.