The literal translation of "能ある鷹は爪を隠す" is “The wise hawk hides its talons.”
But what should I understand the proverb as meaning? Is it just about humbleness, or about not letting your adversaries know what you're capable of?
Sometimes the moral of a proverb could be vague and ambiguous.
The author of this page believes that it tells people to "behave humbly", while this one argues that it means "wise people know how to let others' guard down", which is more or less faithful to what original hawks are said to do. There's also a QA forum answer gives an insight that "truly talented people don't need to show them off because they know they can exert it anytime they want". And this writer is apparently unsure about the true connotation of this idiom:
能力を隠すのは、 They hide their abilities...
そのほうがカッコいいから？ because it's cool?
まわりの人とうまくやっていくため？ to get along with others?
出る杭（は打たれる）にならないため？ because don't want to be "the nail sticks out"?
人を油断させるため？ to let their guards down?
人に利用されないため？ not to be taken advantage of?
能力をひけらかす必要などないから？ because they don't feel a need to show off?
人間としての成長を目指すため（謙譲の美徳）？ for character building (humbleness)?
After all, perhaps it could be concluded that the spirit of a proverb resides in how they understand it.
P.S. I can't keep hiding the fact that I've incidentally used this expression recently :D