Multiline Navigationbar Title

This is doable in a storyboard. Just drag a UIView into the Navigation bar, then drag a UILabel onto it in the document outline, set lines to 2 and alignment to center.

Here is a code example of how you can create a multiline navigationBar title

let label: UILabel = UILabel(frame: CGRectMake(0, 0, 400, 50))
label.backgroundColor = UIColor.clearColor()
label.numberOfLines = 2
label.font = UIFont.boldSystemFontOfSize(16.0)
label.textAlignment = .Center
label.textColor = UIColor.whiteColor()
label.text = "This is a\nmultiline string for the navBar"
self.navigationItem.titleView = label

Swift 5.x:

let label = UILabel()
label.backgroundColor = .clear
label.numberOfLines = 2
label.font = UIFont.boldSystemFont(ofSize: 16.0)
label.textAlignment = .center
label.textColor = .white
label.text = "This is a\nmultiline string for the navBar"
self.navigationItem.titleView = label