The following example shows how to apply custom fonts to a Navigation Bar and includes fixes for some quirky behaviors found in Xcode. One also may apply the custom fonts to any other UIControls such as UILabels, UIButtons, and more by using the attributes inspector after the custom font is added to the project. Please note the external links to working samples and videos near the bottom.
(You will likely need to toggle the Bar Tint for the Navigation Bar before Xcode picks up the new font)
Verified that this does work on Xcode 7.1.1+. (See the Samples below)
Some of these are repeated which means they are very likely worth noting.
Note ~ A nice checklist can be found from the Code With Chris website and you can see the sample download project.
If you have your own font and want to use that in your storyboard, then there is a decent set of answers on the following SO Question. One answer identifies these steps.
So Xcode naturally looks like it can handle custom fonts on UINavigationItem but that feature is just not updating properly (The font selected is ignored).
To workaround this:
One way is to fix using the storyboard and adding a line of code: First add a UIView (UIButton, UILabel, or some other UIView subclass) to the View Controller (Not the Navigation Item...Xcode is not currently allowing one to do that). After you add the control you can modify the font in the storyboard and add a reference as an outlet to your View Controller. Just assign that view to the UINavigationItem.titleView. You could also set the text name in code if necessary. Reported Bug (23600285).
@IBOutlet var customFontTitleView: UIButton!
//Sometime later...
self.navigationItem.titleView = customFontTitleView
Note - This example is derived from an answer I posted on SO (here).