The blockchain is C++ (bitcoin fork)
The SDK is python
The apps are JS (desktop/lbry.tv/odysee.com), and java/swift for mobile apps.
The disk space issue is definitely something that has been talked about for a while. https://github.com/lbryio/lbry-sdk/issues/1311. As the lead maintainer of https://github.com/lbryio/lbry-desktop, it's the last issue I'm waiting on before the 1.0 release!