- #Python is written in C
- #Perl is written in C
- #Ruby is written in C
- #PHP is written in C
- #JavaScript engines started in C, now mostly in C++
- #Go was first in C, now written in Go itself
- #C++ compilers are written in C++
- #Swift is built with C++ and Swift (on LLVM in C++)
- #C# runs on .NET, built in C++/C#
- #JVM (HotSpot) is written in C++

Yet, people still doubt the necessity of learning C!