Well, according to professor Bańko, they're usually interchangeable, but when you can always change "za" to "zbyt", it won't always be possible the other way round.
He says that it has to be "zbyt" when you have an adjective derived from a verb, or when it's an adjective derived from another adjective by negating it with a 'nie-' prefix. And probably in some other examples, but even for him it's hard to give more rules on finding them.
Hi marek. Could you give an example of an adjective from a verb, and an adjective from another adjective, please?
Well, I believe that 'an adjective from another adjective' would be mostly negated adjectives, like "niesmaczny" (not-tasty). "za niesmaczny" indeed sounds weird to me.
An adjective derived from a verb would be for example "znany" (known), from 'znać' (to know).
Oddly, saying that stuff is "dear" or "too dear" seems to be falling out of use, at least in my quadrant of the planet. Nevertheless, I suggest that it should be accepted. You could report, but our tireless mods will probably pick it up from this conversation.
We started accepting it some time ago, but apparently it hasn't worked here so far. Added now.
It sounds very strange to my EFL ear, I have to say. I heard it today in "The Crown" and I wonder if it wasn't the first time ever for me.
Quite. Your "EFL ear" is working well. Its use in this context is quite old-fashioned, and somewhat restricted. There is a danger of confusing "dear", meaning "expensive", and "dear, meaning "beloved", so I guess the former meaning is dropping out of use.