The Chelsea skipper, who retired from international football amid the Anton Ferdinand affair, is back near his best in Mourinho's second spell in charge.
At present, Terry and Brazil defender David Luiz are keeping England first-choice centre-back Gary Cahill out of the starting line-up.
Mourinho has no doubts about former England captain Terry's quality but so far discussions with the 32-year-old - one of the few players at the Blues' Cobham training base during the international break - have focused on fitness.
"I've not spoken with him about it (England)," Mourinho said.
"I just tried to recover his status as an important player.
"When a player plays for a big team it's because he's good enough to.
"Rio Ferdinand plays for Manchester United. If he plays for Man United, he's ready for the national team.
"John Terry. When you play for a big team, you are ready for the national team.
"But the problems that ended with the player stopping to go to the national team, that's not my problem, that's not David Moyes' problem, that's not a manager's problem. It's a personal thing."
Earlier this year it was suggested Terry would consider an international return, something Mourinho says is a matter for the player and England boss Roy Hodgson.
The Chelsea boss said: "I'm not in favour or against. It's their decision."
Terry has been boosted by Mourinho's return, having missed some key fixtures under last season's interim boss Rafael Benitez, who preferred Branislav Ivanovic at centre-back.
"He had a bad season," said Mourinho, who views Ivanovic as a right-back.
"Sometimes self-esteem is a bit attacked. In this moment he is fine.
"It doesn't mean he will always be first choice with me, but he knows that I trust and am happy with the way he's performing."
Mourinho does not like leaving Cahill out, but insists he will get his chance and his England hopes will not be compromised by a lack of action at club level.
"I would never do something that could jeopardise his selection for the national team," Mourinho said.
"He is going to play a lot and who knows, in a couple of weeks I may change my mind because of performances and he becomes my first option and I leave John or David out."
In World Cup year, players are even more keen to play and impress.
Mourinho added: "I have to think about Chelsea but I also have to think about them and their national teams, because it's important to them.
"When a player is not selected for the national team he is sad and when a player is sad a player he can't perform for Chelsea the same way he performs if he's happy.
"It's all connected. In the case of Gary, I have to make him happy, I have to make him play, he has to go to the national team and Roy has to be happy."
Terry and Luiz are expected to start against Cardiff on Saturday.
Terry is synonymous with Chelsea and it is unthinkable he might line up in a red shirt.
Cardiff changed their colours from blue to red at the behest of Malaysian owner Vincent Tan.
Mourinho says Roman Abramovich, the Chelsea owner, would be within his rights to do the same if he wished.
"It's his club, let's go in red," Mourinho said.
"If Mr Abramovich decides to change the colour to red or yellow or whatever, we would always be the Blues. Even with red shirts."
Tan recently replaced head of recruitment Iain Moody with 23-year-old Kazakhstani Alisher Apsalyamov, who was previously employed painting Cardiff City Stadium.
Asked how he would feel about a similar appointment at Chelsea, Mourinho said: "Age is not a problem. If he paints well..."