There is no one language to do all that. Writing desktop applications will require different languages and compiler than writing web based applications. And writing mobile applications is still different from either of the other two. First determine what it is that you want to write and then select a language and compiler (if needed) to produce it. There's no "one size fits all" here.
to devolop software like:
1. any OS - C/C++
2. application software - Any Language Can do!
3. IDEs - Any language can do (CodeLite in C++, Wing IDE in Python, IntelliJ Idea in Java et al)
4. computer - Answered as no 2
5. mobile applications - Most of themw will do (C++ in Symbian, Python in S60, Java ME et al)
That is a bit field, so I can't really speak for all of it since I don't know.
First off there are not that many completely distinct OS , we have windows, unix (several flavours0, linux, BSD/Mac OS-x then stuff like OS-9 [it is in things like microwaves, digital watches, videos, washing machines -- if anyone knows the install base numbers please let us know! -- I have half an idea it might be the most popular OS, but don't know.
All of those have some assembly, a lot of C, some like windows have C++, which might be the dominate coding language (?). Cool operating systems like VMS, had BLISS which was the popular operating system language BEFORE C came along!!!
The real question is why do you want to know, and specifically in what area do you want to know. That would give a much more focused answer. [Note: idol curiosity is perfectly acceptable...]
Since you posted this to the C++ forum, the general overall, how has paying jobs coding would indicate that, java leads and c++ is around the 15% mark.