What key aspect do language keys support in Liferay applications?

Language keys are an essential component of Liferay applications that primarily support internationalization (i18n). Internationalization refers to the design and development of applications in a way that enables them to be adapted to various languages and regions without requiring significant changes to the source code.

By utilizing language keys, developers can create a single version of their application that can present content in multiple languages based on user preferences or locale settings. Language keys serve as placeholders for text strings, allowing for easy substitution of the displayed text depending on the selected language. This is crucial in making applications accessible and user-friendly for a global audience, as users can interact with the application in their preferred language.

The other options, while important aspects of application functionality, do not specifically relate to the role of language keys. Speed of application loading is more tied to optimization strategies rather than internationalization. User authentication pertains to access control and secure login processes. User engagement is a broader concept that encompasses various strategies for maintaining user interest, which isn't directly connected to the function of language keys in supporting multiple languages within Liferay applications.