Any language running on the JVM (Java, Kotlin, etc.) and CLR (C#, VB.NET, etc.). As long as you don't compile directly to native code and you aren't running in a locked-down environment where codegen is disabled, you can generate code at runtime and execute it alongside existing code.

For example, there's java.lang.reflect.Proxy [1] and System.Reflection.Emit [2].

[1]: https://docs.oracle.com/javase/8/docs/technotes/guides/refle...

[2]: https://learn.microsoft.com/en-us/dotnet/api/system.reflecti...