What do you mean with "is the language open source"? The Ada specification is public [0] but not open source -- but the C and C++ specifications are not open source either, in the normal sense of the term. And like with C and C++, there are both open source and proprietary compilers for Ada, see e.g. [1]
What's mostly not open source (FAFAIK) is SPARK, the formal verification framework for Ada.
SPARK tools are also open source. The main tool `gnatprove` is based on GCC as well. https://github.com/AdaCore/spark2014
It's not a community project, AFAICT. Few people know how to build it from source.
That links gives me a 404. Does it require membership of some organization before you're allowed to view it?
edit: did you mean https://github.com/AdaCore/spark2014 ?
Sorry, yes 2014. Fixed it.
The C++ (draft) standards are open source:
https://github.com/cplusplus/draft
Last time I looked I could not find an equivalent repository for the C standards.
There isn't one. They publish completed drafts on the working group website:
https://www.open-std.org/jtc1/sc22/wg14/www/wg14_document_lo...
.pdf unfortunately. The C++ sources that I linked to are machine readable .tex.