Google Sites is very easy to design, so if you want additional language on your site, you can simply copy the entire site and translate it with different languages.
You'll need a custom domain once you've translated your site.
Here's how you can add an additional domain to your Google Domains account for your 2nd language Google site.
Say you already have www.yourbusiness.com as your main landing page, but you want to have ko.yourbusiness.com for the Korean version.
As a first step, please add a custom domain ko.yourbusiness.com to your Google Sites settings. Note that only the owner of google sites can add a domain under settings.
Next thing is logging into your Google Domains account, select the domain name and go to the 'Website' page to add a subdomain. Click on 'Build another website'