Support device locale on app startup

src/locale/deviceLocales.ts

@@ -41,11 +41,13 @@ export function getLocales() {
   return output
 }
 
+export const deviceLocales = getLocales()
+
 /**
  * BCP-47 language tag without region e.g. array of 2-char lang codes
  *
  * {@link https://docs.expo.dev/versions/latest/sdk/localization/#locale}
  */
 export const deviceLanguageCodes = dedupArray(
-  getLocales().map(l => l.languageCode),
+  deviceLocales.map(l => l.languageCode),
 )

src/locale/helpers.ts

@@ -181,3 +181,19 @@ export function fixLegacyLanguageCode(code: string | null): string | null {
   }
   return code
 }
+
+/**
+ * Find the first language supported by our translation infra. Values should be
+ * in order of preference, and match the values of {@link AppLanguage}.
+ *
+ * If no match, returns `en`.
+ */
+export function findSupportedAppLanguage(languageTags: string[]) {
+  const supported = new Set(Object.values(AppLanguage))
+  for (const tag of languageTags) {
+    if (supported.has(tag as AppLanguage)) {
+      return tag
+    }
+  }
+  return AppLanguage.en
+}

src/state/persisted/schema.ts

@@ -1,6 +1,7 @@
 import {z} from 'zod'
 
-import {deviceLanguageCodes} from '#/locale/deviceLocales'
+import {deviceLanguageCodes, deviceLocales} from '#/locale/deviceLocales'
+import {findSupportedAppLanguage} from '#/locale/helpers'
 import {logger} from '#/logger'
 import {PlatformInfo} from '../../../modules/expo-bluesky-swiss-army'
 
@@ -131,7 +132,10 @@ export const defaults: Schema = {
     postLanguageHistory: (deviceLanguageCodes || [])
       .concat(['en', 'ja', 'pt', 'de'])
       .slice(0, 6),
-    appLanguage: deviceLanguageCodes[0] || 'en',
+    appLanguage: findSupportedAppLanguage([
+      deviceLocales[0].languageTag,
+      deviceLanguageCodes[0],
+    ]),
   },
   requireAltTextEnabled: false,
   largeAltBadgeEnabled: false,