This booklet is promoting the constructed language Esperanto in Belgium and The Netherlands. Esperanto was invented by the Polish writer, L.L. Zamenhof. He grew up fascinated by the idea of a world without war and believed that this could happen with the help of a new international auxiliary language, which he first developed in 1873 while still in school.
This booklet was made by Frits Faulhaber and Th. Buis (ed.) and was published in 1935. You can notice typographical characteristics from Bauhaus and De Stijl. These artistic movements aspired pure abstraction and universality by a reduction to the essentials of form and colour — which aligns with the purpose of Esperanto as a universal language.
The language is still in use today. Up to 2,000,000 people worldwide, to varying degrees, speak Esperanto. In 2012, Google Translate added Esperanto as its 64th language. (Wikipedia)