The new United manager has already made an impression in his short time in the job, trying out a new 3-5-2 system and even challenging the club on their commercial policy.
And the Dutchman's latest edict is that players should speak to each other in English.
"We only speak in English," said Mata, speaking on the club's tour of the United States. "He (van Gaal) says we have to speak in English.
"He is very good on and off the pitch. He is a good man and a great manager.
"He has a lot of experience; he has won trophies in previous teams too, so it's a good chance for me to learn from him and for us to improve as a team.
"He is demanding. He is very honest, straight, speaks with everyone to his face. I think this is good, a perfect way to do it, saying what you think about the players in front of them."
The Spaniard had the unfortunate experience of watching from the bench as van Gaal’s Netherlands team beat Spain 5-1 in their opening game of the Brazil World Cup this summer.
"That game was very, very bad for us," said Mata. "They scored five goals against Spain so he did a great job."
It was during the later stages of the World Cup that van Gaal first implemented a 3-5-2 to great success, and his first experiment with the formation at United yielded a 7-0 win over LA Galaxy this week.
Mata believes the new system could mean a chance to play in his favoured position behind the strikers, a role in which he twice won Chelsea's Player of the Year award.
United's record signing at times looked less assured on the wing under David Moyes, and he said: "If I play behind the two strikers it's a good position (for me). I can look for the ball, I can try to assist or score, so I will try my best.
"I will try to score as much as I can and try to help the team from that position.”
Tom Cleverley is also welcoming the changes brought in by the new boss.
The midfielder, who got two hefty pats on the back from van Gaal as he sat by him during the pre-match press conference ahead of a friendly against Roma, said: "I watched Holland in the World Cup and I think I can be his type of player.
"I have to show that in training and most importantly in the games. I think there is a place for me. I have to prove that."