Well, call me a geek but Vultus est index animi has long been one of my favourite expressions.
And now I know it in Spanish as well:
Los ojos son el espejo del alma.
Now all I need to do is Cautus metuit fovea lupus in Spanish and I’ll be happy.
All you need are a few handy expressions in other languages to sound intellectual, witty and ever so.
Or alternatively like you are a total numpty desperately trying to impress.