You do not. The dragon language is made by Bethesda Softworks. We are not Bethesda Softworks, therefore we do not change it.

This has not always been so, though. The Legacy Dictionary was compiled by site members in a more adventurous time, and is kept for its utility in informal contexts. Official site events will never require Legacy vocabulary, but you are free to use it in conversation or works of art if you so choose.