You're talking about two different "tail call optimizations" here.
Scala supports local tail call optimization for a single function. A lot of FP languages support mutually recursive tail call optimizations, where two functions recursively call each other (common in FP). Scala (and no JVM language to my knowledge) cannot optimize this and so programmers have to resort to workarounds like Trampolines.
In contrast, LLVM IR and .NET CLR support it, allowing language compilers to use it. F# supports it and there's plans for C# to support it. It might be supported in the LLVM Scala target (Scala native) at some point in the future.
Scala supports local tail call optimization for a single function. A lot of FP languages support mutually recursive tail call optimizations, where two functions recursively call each other (common in FP). Scala (and no JVM language to my knowledge) cannot optimize this and so programmers have to resort to workarounds like Trampolines.
In contrast, LLVM IR and .NET CLR support it, allowing language compilers to use it. F# supports it and there's plans for C# to support it. It might be supported in the LLVM Scala target (Scala native) at some point in the future.