die Worthülse — a word husk, a phrase with nothing inside.
heiße Luft — hot air.
schwafeln — to waffle, to talk at length and say nothing.
der Phrasendrescher — a phrase thresher, someone who threshes stock phrases.
die Sonntagsrede — a Sunday speech, fine words with no consequences.
der Wichtigtuer — someone who makes himself important.
mitreden können — to know enough to join in. Da kann ich nicht mitreden means: I don’t know enough about that to say anything.