Serbian language fallback

We want to implement Serbian (latin) language in our app. The idea is pretty simple: if user device's preferred language is Serbian (no matter, latin or cyrillic) – we use Serbian latin, which we have in our app.

The problem is that it looks like this idea is unimplementable. If we use sr_Latn as code for Serbian latin in our Info.plist, and device's preferred language is just Serbian (which is Cyrillic in iOS) – the fallback in app will be English (default language), not Serbian latin. Reverse is the same: if we implement Serbian latin as sr (just Serbian), then user select Serbian latin (sr_Latn) as device's preferred language – then app language will be English, not Serbian.

In the source code published on one of the forum's answer I see that it is expected fallback (unfortunately undocumented). This code is old one, but looks like behavior still persist.

Is there any way to implement one Serbian for all cases?