Here is a collection of puzzles I've written about real-world languages, similar to the puzzles from the International Linguistics Olympiad. Theoretically, they require no prior knowledge of language or linguistics to solve (although experience with how different languages work is of course helpful).
2018-1-prob.pdf This set of problems is written in the same format as the individual IOL contest, but they are easier. There are no solutions written yet.
zoque-1-prob.pdf This single Rosetta stone problem is approximately the difficulty of an IOL problem. Solution (with full explanation)
Here are some other places you can find problems similar to these: