We have a simple language switcher that works for the admin content. You just need to add this parameter to the URL in the front end:
?wpfa_admin_language=en_US (or other languages) and the admin screens will load in that language.
Notes:
- Make sure that the language is installed in WordPress. You can go to wp-admin > settings > general options, and see if the language is installed
- The admin screens will use the translations provided by the plugins or from WordPress.org (automatic translations). If a plugin doesn’t provide translations for that language, the texts of the specific plugin won’t be translated.
- You can translate or edit the translations of plugins/themes editing their .po and .mo files using poedit or any .po editor.
How can you use this in the front end?
You can add some flag icons to your dashboard menu in the front end, and the flag icons can link to the current page containing the ?wpfa_admin_language=language parameter. So the user will be able to easily change the language.
If you use a multilingual plugin like WPML/Translatepress/Polylang, you can also add the parameters that those plugins use to change the front end language, so your menu links can have both, for example, if your multilingual plugin uses the parameter ?lang= to change the front end language, you can combine them like ?lang=xx&wpfa_admin_language=xx to translate both the front end and backend screens at the same time.
