From what they have written, the only other language that meets their requirement seems to be
Ada:
1. Stability: Ada is an "old and boring" language (aka stable and reliable - the first standard for the language was issued in 1983 and created for the Defence industry) - https://learn.adacore.com/courses/intro-to-ada/chapters/intr...
2. Compatibility: Interoperability features is built-in, allowing you to create Ada libraries that can be used with other languages - https://piembsystech.com/interfacing-ada-programming-with-c-...
3. Embedded Programming: Ada has been designed for embedded programming and the language includes constructs for directly manipulating hardware, for example, and direct interaction with assembly language. - https://learn.adacore.com/courses/intro-to-embedded-sys-prog...
4. Ada supports processes / suites to comply with Branch coverage in ISO 26262 ( https://github.com/NVIDIA/spark-process ) and Decision coverage in DO-178C ( https://learn.adacore.com/booklets/adacore-technologies-for-... ).
5. Ada has features supporting memory safety to avoid many memory issues in the first place ( https://www.adacore.com/blog/memory-safety-in-ada-and-spark-... ) and using its exception handling and programming techniques (like pre-allocating "guard" memory) can allow Ada programs to tackle fringe OOM errors.
6. Performance: Ada is built for systems programming, is just as fast as C ( https://learn.adacore.com/courses/Ada_For_The_Embedded_C_Dev... ), with the added bonus of "modern" programming features that can generate more "reliable" code