For me, the high point of the International Mother Tongue Day was the request for the fourth and final part for the localisation of MediaWiki in Telugu. I am really impressed with all the hard work that makes such a difference for the usability of our projects.
It is a well established fact that providing information in someone's mother tongue is most effective. With a Wikipedia where both the User Interface and the content are available in the same language we provide the best environment possible. When this is realised it is "just" a matter of maintaining and improving the quantity and quality of the project.