Add language switcher and translated content to Vue/Nuxt website

Our company website has been English only since we launched it about three years ago. It's a Nuxt 2 front end with a small Node.js backend that serves the content from a JSON based store. A friend of mine built it, and he has since moved to another country and isn't available for this. Now we're expanding to Germany and Spain, so the site needs to be available in three languages: English, German and Spanish. We already have professionally translated copy for the main pages, in spreadsheets. What's missing is the plumbing. A language switcher in the header, URLs that make sense (for example /de/ and /es/ prefixes), and the content actually showing up in the chosen language. What I imagine, but I'm open to better ideas: use nuxt-i18n or something similar for the static text on the pages, and extend the backend so that the dynamic content (the blog and the product pages) can store a translation per language. The language should be remembered if a visitor comes back, and ideally we'd also have the right hreflang tags so Google doesn't get confused. I can give you access to the repository, a staging server and the spreadsheets. Right now I don't expect big design work, just the switcher itself to look decent on desktop and on mobile. If something in the current code turns out to be a mess, tell me early rather than quietly working around it. Also, a few pages have text hardcoded inside components, so expect some digging. When it's done I'd like a short explanation of how I add a fourth language later, because the Italian market is next.