If you create and disable (e.g. @IBOutlet var barButton: UIBarButtonItem! ) UIBarButtonItem with your UIBarButtonItem , you can change your font type using setTitleTextAttributes in the output.
barButton.setTitleTextAttributes([ NSFontAttributeName: UIFont(name: "Arial", size: 12)!], forState: UIControlState.Normal)
Swift3
barButton.setTitleTextAttributes([ NSFontAttributeName: UIFont(name: "Arial", size: 12)!], for: UIControlState.normal)
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