The Rainbow is connected with different mythologies in different cultures for it's seen all around the world. And seven colors in it stand for diversity, beauty, etc..
My design here is inspired by the rainbow to illustrate how diversified languages are. The brown rectangle means soil--"Cultural" which nurtures the branches. The colors are shining on different branches--"languages" which are emphasized around us. But there are also large branches unshined by colors which means the less known languages in our world. And both black lines means that these not so popular languages are in danger because they seperate branches from the soil. And even for those shining branches, their roots are unshined to mean that they're also somehow in danger.
The polygon is reserved for the UNESCO mutiple languages logo. The slogan, the date, and the name of the celebration are all marked in brown to mean that whether you're kids or adults, if you take part in this celebration, you can add the color to branches to reveal their true values of existence--lives, not colors.