C compatibility is one of the original design goals for Swift and is used extensively for the Linux version, for making Swift wrappers around existing libraries, and the Objective-C bridge on macOS. If using Xcode, one would use a bridging header; otherwise, one can use Swift Package Manager to wrap C libraries for use in Swift projects.

Swift recently gained the features needed to call Python code. You can either use the Python module from Swift for Tensorflow or the PythonKit library, both of which allow calling Python code from within Swift.

The features used to allow calling Python from Swift can also be used for other dynamic languages, so there may be the ability to call Ruby and other languages' libraries in future as well.