A leopard can't change its spots
vilɡ zmʲɛɲi skurɛ alɛ xaraktɛru ɲʲɛ
In Polish Wilk zmieni skórę, ale charakteru nie.
This Polish idiom, meaning 'The wolf will change its skin, but not its character,' is similar in meaning.
Example
"On próbował się zmienić, ale wilk zmieni skórę, ale charakteru nie."
