[Regional Preference] Fix subtitle overlap

 - Avoid to generate a new locale with extra U extension.
 - Get correct LocaleInfo from LocaleStore.
 - Avoid to show language tags on system language page

Bug: b/267268410
Bug: b/267415412
Bug: b/267408059
Test: Manual test passed.

Change-Id: I53e7b8d50f81c1887985a313086ca424e0fc24d7
1 file changed