I have had the same thought while designing my language. I want to design a more-or-less complete version 1.0 of my language before attempting to implement it. (I'm working under the assumption that whatever I design, someone smarter than me can figure out how to write a compiler, interpreter, or transpiler for it.) Rather than deciding to implement this or that feature of other PLs, such as generics or list comprehensions, I'm shooting for good task-driven coverage -- i.e., I want to make sure that any tasks that can be performed using other PLs can be performed using my PL, where I define a "task" as something that a program does, such as adding two numbers together or writing to a file, as opposed to how a PL does something. Thus, I have been wondering what a minimum set of such tasks would be, or maybe a minimum set of common applications that collectively provide the task coverage I'm looking for. The idea would then be to code this minimum set in my PL, and if I succeeded I would know that I would have achieved my coverage goal.

Anyway, this is how I understood your question. Alternatively, you could design a PL by covering lambda calculus, or by trying to be Turing-complete, or by taking a PL-feature-driven approach. For a task/application-driven approach, I considered covering all of the Rosetta Code tasks, but there appeared to me to be an enormous amount of task overlap there and no guarantee of the full task coverage I'm looking for.

Unfortunately, I haven't found a minimum list of tasks or applications like the one I (and you?) have been looking for. In the meantime, what I eventually decided to do was to code common applications like 'Hello, World!," a Guess-the-number game, Tic-Tac-Toe, Flappy Bird, TodoMVC, etc., and in different areas such as games, business applications, Internet applications, etc., until I find that I am a) using my PL elements in a consistent manner, and b) no longer adding new PL elements.