Constructed languages introduced in the 1900s

Ido () is a constructed language derived from a reformed version of Esperanto, and designed similarly with the goal of being an international auxiliary language (or universal second language) for people of diverse languages. To function as an effective international auxiliary language, Ido was designed specifically to be grammatically, orthographically, and lexicographically regular (and, above all, easy to learn and use). It is the most successful of the many Esperanto derivatives, known as Esperantidoj.

Latin-based international auxiliary language

international auxiliary language, published by the International Academy of the Universal Language in 1902 under the leadership of W. Rosenberger; a heavy revision of Volapük

a priori constructed language

spurious Brazilian language, invented 1901