Latin

I've heard that if you know Latin, that you basically know Italian, Spanish, Catalan, Portuguese, French, and Romanian. I want to know if there is truth to this statement.

There are a couple of linguistic shortcuts with learning Latin, I guess I should have been a little more explicit.

What I said about not just being able to watch movies without subtitles is true.  However, the understanding of grammar and etymologies will help you with learning and memorising future languages to varying degrees.  BUT this can be said of practically any language to a degree, including the more bizarre language isolates like Hungarian.  There might be a hell of a lot less crossover in etymology that is helpful, but even still, knowing what an interrogative pronoun or the accusative case is a handy thing to know for every language.

Learning one language will help you to speed up the learning of others, but it won't teach you the others unless the differences are superficial (see: Serbian and Croatian).  The differences between Latin and its child languages are not superficial.