Well, the 'archaic & poetic' style, as you described it, appears in The Tales of the Robots (aka Mortal Engines + Cosmic Carnival). Also, partly, in Cyberiad.
As for Golem XIV, yes, the difficulties lie in the terminology. Mostly because he uses words that may be hard to understand for most people. Also, the logical structure of the language Golem uses may be hard to follow, as it is very complex.
As for colloquialisms, I don't recall to many examples.