So I have dig down on more research regarding this and this is my conclusion.

For the index page (Home Page) if the URL isn't containing the locale in it i.e `https://webmaker.org` or `https://webmaker.org/` both can be treat the same and we can just leave them like that to return `200` for both and search engine will deal with them because the browser will take off the trailing slash at the end, but in the case of having the locale in it now that would be an issue for two reasons. One the browser would treat this two differently `https://webmaker.org/en-US` and `https://webmaker.org/en-US/` in which if we keep both and returning 200 now it would cause us a duplicate content because search engine would treat them as two different page even though they have the same content. From this official Google Webmaster blog this is how I understood and I believe this is how we should deal with the case of having locale in the URL. (http://googlewebmastercentral.blogspot.ca/2010/04/to-slash-or-not-to-slash.html)

We should do a `301` redirect for the one with trailing slash and redirect them to the one without trailing slash and keep this consistent as the same with the URL that doesn't include the locale in it.

This is base on my research and my opinion.