Yes, bootstrapping with regard to languages is the trick of getting that first compiler running so you can compile the rest of the compiler.
It has been done many times. The first assemblers were written directly in machine language. The first compilers were written in assembly. Many implementations of FORTRAN, ALGOL, COBOL, etc. As late as the 1970s it was not unknown to write a new high level language directly in machine code. Steve Woz's BASIC for the Apple II was "hand-assembled", as he put it.
So, taken literally, certainly not. People still do it today as a hobby or educational project.
But if we take the question in a looser sense? Yes kind of, at least in the UNIXish world. No one has implemented a serious high level systems language, except in a high level systems language, for a long time now. Rust, for example, was initially implemented in Ocaml. And normally that's what would be called the first Rust bootstrap. But OCaml was implemented in C, probably compiled by Clang or GCC. GCC was written in C and... so on.
Often one finds it does lead back to DMR at a PDP-7. On the other hand, I strongly suspect something like IBM's COBOL compiler for their mainframes (still supported and maintained today!) would not have such a heritage.
I'm not an expert, but I guess "bootstrapping" only applies to compilers, and Apple II BASIC was an interpreter. An interpreter doesn't have to compile itself, only run the programs you give it. So on an 8-bit computer the priority is to have an implementation that (a, and most importantly) takes up as little space as possible and (b) is reasonably fast.
The Apple ][ has a monitor in ROM that allows to enter machine code directly. The legend says that for the Apple I, Woz knew the complete integer basic machine code and could type it live into the monitor.
Also, the monitor on pre-][+ machines with integer BASIC also had a mini-assembler, so short assembly programs could be typed in as such instead of keying in the bytes. Both versions of the monitor had a mini-disassembler.
On the other hand, I still remember at least a few 6502 hex opcodes, not that I have any use for that information anymore. The instruction set is small enough that it doesn't surprise me that Woz would have it memorized.
I’m not aware of any basic that is implemented in itself. There must be one or two somewhere, but typically for systems like the apple ii or Commodore PET, basic was implemented always in assembly.
So most weren’t exactly bootstrapped the way we are talking here.
> No one has implemented a serious high level systems language, except in a high level systems language, for a long time now.
LuaJIT is a prominent counterexample. The base interpreter in written in assembly for performance. It comes with its own tradeoffs, especially portability.
LuaJIT uses it's DynASM library for both static and JIT code generation. DynASM is implemented in a mixture of Lua and C, and Lua is of course implemented using C. So LuaJIT actually depends on a C compiler to generate assembly. Plus, not all of LuaJIT is implemented using assembly, only some critical hotspots (e.g. the bytecode interpreter loop). The rest is just C.
DynASM is actually really cool.
I almost forgot: apropos bootstrapping, because LuaJIT requires Lua to build, it includes a single-file, stripped down version of PUC Lua 5.1 which it can build to bootstrap itself if the host lacks a Lua interpreter.
It has been done many times. The first assemblers were written directly in machine language. The first compilers were written in assembly. Many implementations of FORTRAN, ALGOL, COBOL, etc. As late as the 1970s it was not unknown to write a new high level language directly in machine code. Steve Woz's BASIC for the Apple II was "hand-assembled", as he put it.
So, taken literally, certainly not. People still do it today as a hobby or educational project.
But if we take the question in a looser sense? Yes kind of, at least in the UNIXish world. No one has implemented a serious high level systems language, except in a high level systems language, for a long time now. Rust, for example, was initially implemented in Ocaml. And normally that's what would be called the first Rust bootstrap. But OCaml was implemented in C, probably compiled by Clang or GCC. GCC was written in C and... so on.
Often one finds it does lead back to DMR at a PDP-7. On the other hand, I strongly suspect something like IBM's COBOL compiler for their mainframes (still supported and maintained today!) would not have such a heritage.