You should never attempt to manipulate the UITabBar object itself stored in
this property. If you attempt to do so, the tab bar view throws an exception.

for (int i = 0; i < [self.tabBarController.viewControllers count]; i++) {
    if([self.tabBarController.viewControllers[i] isKindOfClass: [UIViewController class]]) {
        UIViewController *vc = self.tabBarController.viewControllers[i];
        switch(i) {
            case 0:
                vc.tabBarItem.title = @"primero";
                break;
            case 1:
                vc.tabBarItem.title = @"secondo";
                break;
        }
    }
}