... so is mine after learning Polish :)
Why not his brain?
We differentiate umysł=mind and mózg=brain.
They both mean He is too tired to think, but OK - I understand that the translation should be as precise as possible.
What does it mean? 'He is too tired to think' or what?
Yes, something like that.
More appropriate to say "he is tired and cannot think.
Is this something someone would actually say in Polish? In English it sounds weird.
It's not some common set phrase, but I wouldn't be surprised to hear about "zmęczony umysł".
We say at times : His mind is extremely exhausted
And that seems... quite extreme. Definitely more than just "very tired" ;)
I could see this being said in Poland. Ive found that certain phrases like this get a little poetic or less straightforward.
I found it rather puzzling, as if it was intentionally convoluted, to hide some deeper meaning.