feat(i18n): initialize locale before React (#2343)

* feat: initialize locale before React

* chore: explain react-router-dom hash/search usage

src/hooks/useActiveLocale.ts

 import { DEFAULT_LOCALE, SupportedLocale, SUPPORTED_LOCALES } from 'constants/locales'
-import { useEffect, useMemo } from 'react'
-import { useUserLocale, useUserLocaleManager } from 'state/user/hooks'
+import { useMemo } from 'react'
+import store from 'state'
+import { useUserLocale } from 'state/user/hooks'
 import useParsedQueryString from './useParsedQueryString'
+import { parsedQueryString } from './useParsedQueryString'
 
 /**
  * Given a locale string (e.g. from user agent), return the best match for corresponding SupportedLocale
  * @param maybeSupportedLocale the fuzzy locale identifier
  */
-function parseLocale(maybeSupportedLocale: string): SupportedLocale | undefined {
+function parseLocale(maybeSupportedLocale: unknown): SupportedLocale | undefined {
+  if (typeof maybeSupportedLocale !== 'string') return undefined
   const lowerMaybeSupportedLocale = maybeSupportedLocale.toLowerCase()
   return SUPPORTED_LOCALES.find(
     (locale) => locale.toLowerCase() === lowerMaybeSupportedLocale || locale.split('-')[0] === lowerMaybeSupportedLocale
@@ -29,25 +32,24 @@ export function navigatorLocale(): SupportedLocale | undefined {
   return parseLocale(language)
 }
 
-export function useSetLocaleFromUrl() {
+function storeLocale(): SupportedLocale | undefined {
+  return store.getState().user.userLocale ?? undefined
+}
+
+export const initialLocale =
+  parseLocale(parsedQueryString().lng) ?? storeLocale() ?? navigatorLocale() ?? DEFAULT_LOCALE
+
+function useUrlLocale() {
   const parsed = useParsedQueryString()
-  const [userLocale, setUserLocale] = useUserLocaleManager()
-
-  useEffect(() => {
-    const urlLocale = typeof parsed.lng === 'string' ? parseLocale(parsed.lng) : undefined
-    if (urlLocale && urlLocale !== userLocale) {
-      setUserLocale(urlLocale)
-    }
-  }, [parsed.lng, setUserLocale, userLocale])
+  return parseLocale(parsed.lng)
 }
 
 /**
  * Returns the currently active locale, from a combination of user agent, query string, and user settings stored in redux
+ * Stores the query string locale in redux (if set) to persist across sessions
  */
 export function useActiveLocale(): SupportedLocale {
+  const urlLocale = useUrlLocale()
   const userLocale = useUserLocale()
-
-  return useMemo(() => {
-    return userLocale ?? navigatorLocale() ?? DEFAULT_LOCALE
-  }, [userLocale])
+  return useMemo(() => urlLocale ?? userLocale ?? navigatorLocale() ?? DEFAULT_LOCALE, [urlLocale, userLocale])
 }

src/hooks/useParsedQueryString.ts

@@ -2,10 +2,16 @@ import { parse, ParsedQs } from 'qs'
 import { useMemo } from 'react'
 import { useLocation } from 'react-router-dom'
 
+export function parsedQueryString(search?: string): ParsedQs {
+  if (!search) {
+    // react-router-dom places search string in the hash
+    const hash = window.location.hash
+    search = hash.substr(hash.indexOf('?'))
+  }
+  return search && search.length > 1 ? parse(search, { parseArrays: false, ignoreQueryPrefix: true }) : {}
+}
+
 export default function useParsedQueryString(): ParsedQs {
   const { search } = useLocation()
-  return useMemo(
-    () => (search && search.length > 1 ? parse(search, { parseArrays: false, ignoreQueryPrefix: true }) : {}),
-    [search]
-  )
+  return useMemo(() => parsedQueryString(search), [search])
 }

src/i18n.tsx

@@ -2,7 +2,7 @@ import { useEffect, useState } from 'react'
 import { i18n } from '@lingui/core'
 import { I18nProvider } from '@lingui/react'
 import { ReactNode } from 'react'
-import { useActiveLocale, useSetLocaleFromUrl } from 'hooks/useActiveLocale'
+import { initialLocale, useActiveLocale } from 'hooks/useActiveLocale'
 import { SupportedLocale } from 'constants/locales'
 import {
   af,
@@ -36,6 +36,7 @@ import {
   zh,
   PluralCategory,
 } from 'make-plural/plurals'
+import { useUserLocaleManager } from 'state/user/hooks'
 
 type LocalePlural = {
   [key in SupportedLocale]: (n: number | string, ord?: boolean) => PluralCategory
@@ -82,21 +83,24 @@ async function dynamicActivate(locale: SupportedLocale) {
   i18n.activate(locale)
 }
 
+dynamicActivate(initialLocale)
+
 export function LanguageProvider({ children }: { children: ReactNode }) {
-  useSetLocaleFromUrl()
   const locale = useActiveLocale()
+  const [, setUserLocale] = useUserLocaleManager()
   const [loaded, setLoaded] = useState(false)
 
   useEffect(() => {
     dynamicActivate(locale)
       .then(() => {
         document.documentElement.setAttribute('lang', locale)
+        setUserLocale(locale) // stores the selected locale to persist across sessions
         setLoaded(true)
       })
       .catch((error) => {
         console.error('Failed to activate locale', locale, error)
       })
-  }, [locale])
+  }, [locale, setUserLocale])
 
   // prevent the app from rendering with placeholder text before the locale is loaded
   if (!loaded) return null