This book contains linguistic tasks dedicated to a variety of languages of the world. Solving them does not require special knowledge: most readers most likely do not know Swedish and Georgian, and hardly anyone knows the Dirbal and Straits languages. Nevertheless, you can find the key to any problem by understanding through logical reasoning how the unknown language works and how it differs from Russian. Each problem is accompanied by hints, a detailed solution and, most importantly, an afterword in which interesting linguistic phenomena presented in the problem are discussed in more detail. The materials in the collection were published on the popular science website “Elements”, but were significantly revised and expanded for this book. The collection will be useful both for schoolchildren who participate in linguistics Olympiads and for adults who are interested in the languages and cultures of the peoples of the world.