Also, think of the first Yeerk to take a human host. It didn't speak English, that much I can guarantee, yet it had no problem communicating with it and understanding its thoughts (Visser One).
A Yeerk can choose to give a host that same knowledge by the same process. I think that a Yeerk could give a human host all that knowledge instantly, it would just be a matter of whether the human can comprehend it.
In theory though, couldn't the Yeerk also give the knowledge required to comprehend it? For the Z-space example, couldn't they just give everything from basics about space, and every step and component up to a Z-Space transmitter? As long as the human isn't handicapped, he/she shouldn't have a serious problem putting the steps together.
An argument could be that someone takes a math class, yet some people do not understand the math while others do. So yes, it does have it's limits. You can't give a very young or unintelligent person science from basic chemistry up to advanced theoretical physics, and expect them to make head or tails of it.