For real-time embedded there are basically 3 options, C, C++ and Rust. And Rust isn't that widely used, so my guess would be on C/C++. You can't have a GC.
True, I forgot about Ada. While ugly, Ada2012 is a very modern language with a lot of benefits compared to C, especially for embedded control systems programming.
Ada got a bad rap in the past and didn't spread very wide outside US military circles. But it is a very good language. For adoption today it would need some big backing though.
