How to structure URLs for language localized marketing and admin pages

So I have let's say 20 languages the marketing pages of the website are localized into. I am thinking of doing this...

mywebsite.com/en/page-1
mywebsite.com/en/page-2
mywebsite.com/zh/page-1
mywebsite.com/zh/page-2
...

Actually, instead of putting the latin script in there, I would really do this:

mywebsite.com/english/page-1
mywebsite.com/english/page-2
mywebsite.com/中文/页一
mywebsite.com/中文/...

The reason for that is it gives an SEO benefit I would think, for the native language pages.

But now we move onto the admin panel. The admin panel might also have these 20 languages, but should it be structured the same way? Or should it instead be like this:

mywebsite.com/admin/users/1/edit?lang=zh
mywebsite.com/admin/users/1/edit?lang=en
....

Or better yet, just store the language in localStorage and clean up the URL completely.

The reason we do it this way is because these pages are all hidden anyways from search engines, so there's no SEO benefit to be had. Is this the correct way to handle both situations? Or what is best?