>>>As the old latin proverb goes, "wolf changes hair, not the character" (although in the Svetonius's book it's a fox - "vulpes pilum mutat, non mores").
>>
>>In dutch: A fox would lose its hair, but not its character.
>
>In English : A leopard doesn't change it's spots

its spots.

In Russian

Сколько волка не корми, все в лес глядит.

Although this is not the exact meaning or translation. I am trying to remember if there is an exact same saying and can not remember one.