question regarding setting up a version of website in another language

Hi I am setting up a WordPress website for a client at the moment. (This is a single installation wordpress site)

They have asked if I can setup a Spanish version of the site for them as some website viewers will non english speaking. This is for people viewing the site, not the actual people managing the site.

I haven’t done this before, wondering what is the easiest option to offer them.

Thanks

David