Need WordPress advice

I have a new customer who has an English and Spanish version of his website. I am migrating it to new servers.

The english version is at www.whatever.com, and the spanish is at www.whatever.com/espanol.

He has a full wordpress installation in both of these locations, so one in the root, and another one in the espanol folder.

Is this the right way to do this or is there a better solution?

A customer site was in Portuguese. Then they wanted an English version of it. So I did what you just described, I had /english /spanish and so on.....what happened? Google decided the site was in spanish, cuz it's too close to portuguese, then the whole thing became impossible to SEO.

What I do now is have separate domains, even hosted i separate countries for extra local juice.

EDIT: Also don't go anywhere near the wordpress multilanguage plugins. They mess up the content database in irreversible ways. I destroyed a website that way and had to write an app to try and recover the original WP database from the mess the multilanguage plugin made.

For a website in 3 languages, i used a multilingual plugin : wpml (dot) org
and i had no problem for seo
the website ranks on these 3 languages

Personally, I think a subdomain would look nicer for this particular purpose. Like how Wikipedia does it. However, I think the current option is better in terms of SEO. Because it's a subfolder of the actual domain, and gets the proper Domain Authority score and everything. I could be wrong though, someone correct me if I am

There are certain WordPress plugins out there that can manage the Language differences of each countries, however you can still do it manually by recreating versions of your site, though I wouldn't really recommend that.

en.domain.com (english)
es.domain.com (spanish)
de.domain.com (german)
fr.domain.com (french)