material-components_material-components-ios/components/Typography/docs/advanced-use.md

Custom Fonts

Material Components for iOS allows you to set your own font for all of the components. Use the class method setFontLoader: on MDCTypography to specify a loader that conforms to the MDCTypographyFontLoading protocol.

If you want to use the system font use MDCSystemFontLoader which already conforms to the MDCTypographyFontLoading protocol. It is used if no font loader is set.

Swift

class CustomFontLoader: NSObject, MDCTypographyFontLoading {
  func regularFont(ofSize fontSize: CGFloat) -> UIFont {
    // Consider using MDFFontDiskLoader to register your font.
    return UIFont.init(name: "yourCustomRegularFont", size: fontSize)!
  }
  func mediumFont(ofSize fontSize: CGFloat) -> UIFont {
    // Consider using MDFFontDiskLoader to register your font.
    return UIFont.init(name: "yourCustomMediumFont", size: fontSize)!
  }
  func lightFont(ofSize fontSize: CGFloat) -> UIFont {
    // Consider using MDFFontDiskLoader to register your font.
    return UIFont.init(name: "yourCustomLightFont", size: fontSize)!
  }
}

...

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {

  // Before any UI is called
  MDCTypography.setFontLoader(CustomFontLoader())

}

Objective-C

@interface CustomFontLoader : NSObject <MDCTypographyFontLoading>
@end

@implementation CustomFontLoader

- (UIFont *)regularFontOfSize:(CGFloat)fontSize {
  // Consider using MDFFontDiskLoader to register your font.
  return [UIFont fontWithName:@"yourCustomRegularFont" size:fontSize];
}

- (UIFont *)mediumFontOfSize:(CGFloat)fontSize {
  // Consider using MDFFontDiskLoader to register your font.
  return [UIFont fontWithName:@"yourCustomMediumFont" size:fontSize];
}

- (UIFont *)lightFontOfSize:(CGFloat)fontSize {
  // Consider using MDFFontDiskLoader to register your font.
  return [UIFont fontWithName:@"yourCustomLightFont" size:fontSize];
}

@end

...

- (BOOL)application:(UIApplication *)application
    didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
  // Before any UI is called
  [MDCTypography setFontLoader:[[CustomFontLoader alloc] init]];
}