The 27th March was chosen for the International Day of Multilingualism because 27th March 196 BC is the date mentioned on the famously multilingual Rosetta Stone, engraved with Ancient Egyptian, in both hieroglyphic and Demotic text, and Ancient Greek. The Rosetta Stone was the key to unlocking new understanding of Egyptian hieroglyphics because linguists in the 1800s were able to decode the hieroglyphs by translating the Ancient Greek text and comparing it to the Demotic text, looking for overlapping phonic or ideographic clues.
The overlapping of languages, the clues that one language provides for another, and the way that we use languages in a multi-layered, multi-lingual way in our lives has provided the inspiration for the triangles symbol in the logo for the International Day of Multilingualism. Many languages, and many ways of learning and speaking them. All just as valid and valued.
This is what we celebrate on the International Day of Multilingualism.
Multilingual is normal!