Can gallade learn mean look

Answer 1

Yes, in a way.

To get a Gallade with mean look you have to breed for it.

Just breed a Ralts/Kirlia/Gardevoir (female) with a member of the Gastly/Haunter/Gengar (male) that knows Mean Look.
You will get an egg containing a Ralts that knows Mean Look. The Ralts must be male for it to eventually evolve into a Gallade, so you may have to hatch a few eggs until you get one that is male.
Then just raise your newly hatched Ralts until it evolves into Kirlia, use a Dawn Stone on it, and you've got yourself a Gallade that knows Mean Look!