I worked as a civil servant in such a tribunal. Mumps was the first programming language I used professionally - in 2009! I wrote M for a living for around a year. It's still being heavily used in the place I worked at. My colleagues, who were more senior than I by a few decades, had written hundreds of thousands (millions?) of LOC in Mumps and developed a rich ecosystem of internal tools and libraries for it. It was a bit scary to do maintenance work on code that was written in the 80s, but I could often look at the author's signature and find out he was sitting right beside me - still pumping out Mumps. :-)
I can't say I loved the language, but it has some interesting concepts and reading about it makes me feel nostalgic.
Something weird about Mumps that I didn't see others mentioning here is how common it is for M programmers to abbreviate commands. Every command in Mumps can be abbreviated; "w" for "write", "i" for "if"; "s" for "set" and so on. This causes code to be extremely terse, and hard to understand for a beginner. A very simple example:
> I ($G(^ATM(1000))+$G(^ATM(500))+$G(^ATM(100)))<=0 D
> . W #,!,"There is no money available in this Machine. Sorry for the inconvenience."
> . Q
It gets way more complicated than that. After reading this kind of code for a few months, you get really good at parsing it.