iOS using custom Arabic/Cyrillic fonts automatically - ios

Question

I'm trying to learn if it is possible to use a custom Arabic and Cyrillic fonts without having to do a switch/if-else on the user's language setting.
I can successfully use my custom font in the app. I'd like to supply a custom Ar/Cy font the same way, and I know I could build it into the app. If I have my font SpecialFont.otf and also supply SpecialFont-CY.otf how would the OS know to use SpecialFontCY.otf when the user is using a Cyrillic language? Ideally the OS will know the user's primary font and would be able to select a font that matches/includes the correct glyphs for the language.
PS. this is not a question on how to use a custom font, I can do that. I want to know how to supply multiple fonts for various languages to fully support the world without writing code like this:
if NSLocale.preferredLanguages.first == "Arabic"
let myFont = UIFont(name:"SpecialFont-AR", size: 17)
else if NSLocale.preferredLanguages.first == "Russian"
let myFont = UIFont(name:"SpecialFont-CY", size: 17)
...etc

Answer 1

Rather than using a UIFont, you want a UIFontDescriptor. With that you can set the font attribute cascadeList, which tells the system what order to select fonts based on glyph availability (i.e. look in SpecialFont, but if you can't find a glyph for ب, try SpecialFont-CY, and then SpecialFont-AR).
The point of a cascade list is to select the correct font for a given glyph. This way, if a string contains Cyrillic, Arabic, and Latin mixed together, it'll still work fine.
For example:
// Start with your base font
let font = UIFont(name:"SpecialFont", size: 17)!
// Create the ordered cascade list.
let cascadeList = [
UIFontDescriptor(fontAttributes: [.name: "SpecialFont-AR"]),
UIFontDescriptor(fontAttributes: [.name: "SpecialFont-CY"]),
]
// Create a new font descriptor based on your existing font, but adding the cascade list
let cascadedFontDescriptor = font.fontDescriptor.addingAttributes([.cascadeList: cascadeList])
// Make a new font base on this descriptor
let cascadedFont = UIFont(descriptor: cascadedFontDescriptor, size: font.pointSize)
This is covered in detail in Creating Apps for a Global Audience (WWDC 2018).

Answer 2

No you can't, but you can define a simple extension to DRY your code:
extension UIFont {
static func preferred(ofSize size: CGFloat) -> UIFont{
switch NSLocale.preferredLanguages.first {
case "Arabic": return UIFont(name:"SpecialFont-AR", size: size)!
case "Russian": return UIFont(name:"SpecialFont-CY", size: size)!
default: return UIFont.systemFont(ofSize: size) // etc.
}
}
}
Now all you have to do is:
let myFont = UIFont.preferred(ofSize: 17)

Answer 3

You will need to check this somehow in order to determine what is the right language to set.
If you don't want to use if/else syntax, you can use Ternary Conditional Operator.
let myFont = (NSLocale.preferredLanguages.first == "Arabic") ? UIFont(name:"SpecialFont-AR", size: 17) : UIFont(name:"SpecialFont-CY", size: 17)
Or more readable, like this:
let fontName = (NSLocale.preferredLanguages.first == "Arabic") ? "SpecialFont-AR" : "SpecialFont-CY"
let myFont = UIFont(name: fontName, size: 17)