I’m afraid you cannot do that as Cabbage, Csound and JUCE are 3 very different things. What you can do is learn C++ and then start using JUCE. There are some tutorials available here. If however, you wish to produce closed source plugins with JUCE you’ll need to buy a license. Cabbage uses JUCE under the terms of the GNU Public License.
Yeah, WLD-OL is free although it’s not as comprehensive as JUCE. There is no way to convert Csound code to C/C++, but all Csound code is C code in the first place. But the Csound source can be a little overwhelming. I’d suggest you use SoundPipe, or another dedicated DSP library with an appropriate license. If you understand the principals of signal processing in Csound it shouldn’t take too much time to apply them to other frameworks.
I hear you. Cabbage is good for quickly prototyping instruments, and great when it comes to personal music projects. But if you wish to break into the world of audio software development you’ll have no choice but to learn C/C++.