What does this sentence mean?

In this sentence, "up to date" really should be hyphenated ("up-to-date") because it's being used as a collective adjective. It means "current" or "recently updated." For example, if you are using a portable cassette player rather than a discman or iPod, then you are not "up-to-date."

I'm not sure which "specialist language" is being referred to (I'd be very interested to know), but the sentence is saying that teachers, in order to be effective, need the most up-to-date knowledge of this specialist language.