As far as language and text are concerned, I feel (as a vocalist, myself)
that having the music and the text memorized frees you from the score
itself.  I do not feel like I communicate to the audience as well if I have
a score in front of me.  Languages may be hard to learn, but memorizing
Czech or Russian is just like memorizing anything if you know the phonetic
pronunciation and the rules that go along with them.

Stephanie S.