What will be a "Perlis language" will necessarily individual. What makes it so for you, is that it have some features that is conceptually new for you. For me BASIC, C, and Simula was Perlis languages, but none of them has features completly unique to them, but I learned new concepts from them. On the other hand Java, Python and Lua were not, because I had encountered their core features previously, and learned little from them for that reason. People with a different background would have a different experience.
Few concepts are unique to any computer language, so I would argue that it should be about learning new concepts rather that a new programming language.
Some of the examples he picks are rather good at that, since they contain concepts not part of the mainstream paradigms, and so will have new concepts for most programmers.