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12:38 AM
something for you, perhaps I am close: reading locale configuration:
https://android.googlesource.com/platform/packages/apps/Launcher/+/master/src/com/android/launcher/Launcher.java

this shows that only locale is written into config (launcher.preferences), not LocaleData – they are taken from the database
so the question is whether the database is in ROM or whether new records can be added there
(probably device-specific, but what about typical phones?)
 
1:00 AM
(btw connecting the dots: Locale → LocaleData → current locale settings → getting formatted date or time (always using default value) )
 
 
6 hours later…
7:23 AM
first, that's the code of the stock launcher (homescreen) – not an API for locale access. Second, and that might be a pointer, you see what's stored as locale: it's a string (#273), so something like "en_US" or "de_AT", plus the code of the mobile carrier (WTF?).
 

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