Language fixes (#5384)

* Add some comments

* Decouple language settings

* Normalize on read/write

* Refactor

* Support device locale on app startup

* Cleanup, port to web

* Clean up comments

* Comment

* Try not to mutate

* Protect util handling, update test

* Dedupe array values

src/state/session/__tests__/session-test.ts

@@ -10,6 +10,10 @@ jest.mock('jwt-decode', () => ({
   },
 }))
 
+jest.mock('expo-localization', () => ({
+  getLocales: () => [],
+}))
+
 describe('session', () => {
   it('can log in and out', () => {
     let state = getInitialState([])