Use native language names in the language picker

This seems more intuitive to me and is what I've seen in most other
language pickers.

src/services/locale/locale.service.js

@@ -0,0 +1,12 @@
+const specialLanguageCodes = {
+  'ja_easy': 'ja',
+  'zh_Hant': 'zh-HANT'
+}
+
+const internalToBrowserLocale = code => specialLanguageCodes[code] || code
+
+const localeService = {
+  internalToBrowserLocale
+}
+
+export default localeService