I'm confused about medusajs. It has an API but yet I can't find anything about other SDK's. Are you locked into only using JS?
But the source code of the open-source project is written in Node.js, so if you looking to contribute, you are forced to write JS.
Re SDKs, there's an official JS SDK and a community-led Flutter SDK - that I know of. The former can be found in the GitHub repository here: https://github.com/medusajs/medusa/tree/master/packages/medu...
Disclaimer, I am co-author of the project.