To count any language as iPhone language, there are many requirements. One of the important creteria is "dictionary", which is used for spell check, auto-fill, suggestion,... Kannada doesn't have a decent digital dictionary, yet. So, don't even think/dream about Kannada becoming primary iPhone language for decades.
Apple has "other language" category. This would include keyboard, basic translation (mostly copied from Unicode CDLR), a decent font with 5 weights.
Is Kannada even at this "Other language" stage yet. NOPE.
Buggy Font:
Kannada Sangam MN (iOS) and Kannada MN (iOS and macOS) are buggy. Try reading "ಡಾ.ರಾಜ್ಕುಮಾರ್" in iOS device. It will show as "Dr. Rajkurma" not "Dr. Rajkumar". It is a faulty font. These fonts are dead and not updated for years. iOS and macOS are slowly replacing Sangam family fonts which were primarily for Indic languages with Kohinoor family. Kohinoor Kannada font is not seen anywhere, yet.
Keyboard:
There is NO native Kannada keyboard in iOS, yet.
Translation:
For some basic words.
If you are using iOS or macOS for Kannada content. You will have to wait forever to even get these fonts and keyboard fixed/added in iOS and macOS. It is clearly not the prority of Apple.
At best if you wait for another 5 years, Kannada might even qualify as "other language" with native keyboard (to write) and good font (to read). Expect basic entities to read and write, font and keyboard layout!
Dictionary:
It is not Apple's fault, it is largely Kannada people's fault for not developing a decent dictioanary in digital format in past 2 decades. Kannada Ganaka parishat, Kannada sahitya parishat, GoK, and Kannada people are to blame.
my 2 cents.
