To improve programming productivity, the right tools are crucial. This starts with the choice of the programming language, which often predetermines the libraries and frameworks one can use. Polyglot runtime environments, such as GraalVM, provide mechanisms for exchanging objects and sending messages across language boundaries, which allow developers to combine different languages, libraries, and frameworks with each other. However, polyglot application developers are obligated to properly use the right interfaces for accessing their data and objects from different languages.

To reduce the mental complexity for developers and let them focus on the business logic, we introduce user-defined interface mappings - an approach for adapting cross-language messages at run-time to match an expected interface. Thereby, the translation strategies are defined in an exchangeable and easy-to-edit configuration file. Thus, different stakeholders ranging from library and framework developers up to application developers can use and extend these mappings for their needs.