if your goal is to learn new programming languages and libraries, i would suggest Arch, as it has a lot of packages already available for installation. You will save a lot of time, because it is easier to install libraries and header files on it than on debian or fedora (because pkg-lib, pkg-dev, pkg-devlib, pkg-extra, pkg-hell, ...)
Due to its nature, arch will also be a good starting point to understand how your OS works, because you will have to perform some maintenance by hand, while havong a lot of support available thanks to the community.

Now if you want to learn how linux works in-depth, you could try a more "rawish" system like fedora, crux or gentoo. they require more attention and knowledge to be run, but allow for more customizations too, and leave more room to alternatives softwares to try on (changing init system, service managers, and such).