In my native language, which is Polish, there's an expression that describes something I was unable to find in an English dictionary. Today was very sunny and hot in Poland and I was wearing a snowboarding jacket because I didn't check the weather before going out. And then I said to myself "I am dressed too thickly" which is a direct translation from my native language. This is what we say when it's too hot for the clothes we are wearing. There's another expression "I am dressed too thinly" meaning of course that I'm not wearing enough clothes for the cold weather or the clothes I am wearing are not made for such cold weather. So my question is: What would be appropriate phrases to say these in English?
In English, we don't say I am dressed too thickly/thinly.
Instead, we can say:
I am dressed too warmly
I am not dressed warmly enough (we do not tend to say I am dressed too coolly).
However, we do say:
This coat/sweater/shirt/etc. is too thick/thin
We also have the expressions overdressed and underdressed and these are sometimes used to mean dressed too warmly/not dressed warmly enough.
Are You Overdressing Your Baby This Winter?
"It's very hard to overdress a child, and there are minimal side effects of heat exhaustion in the winter, but if children are sweating or act irritable and uncomfortable, you need to reassess them to consider if they are overdressed"
But use these expressions with caution (or don't use them at all in this context). Their more common meaning (or at least the one given by more dictionaries) has nothing to do with the weather:
If you say that someone is overdressed, you are criticizing them for wearing clothes that are not appropriate for the occasion because they are too formal.
You can use overdressed/underdressed in this context if you follow them with "for the weather" or "for this weather" or something equivalent, that would be idiomatic.
"If I'd known it was going to be winter in April, I'd be less underdressed for the weather today"
Otherwise absolutely you can say "not dressed warmly enough"