Implement language switcher / i18n functionality

We need to implement i18n functionality in the website, but there's still some conceptual work, we need to finalize, before we can work on this:

• How do we structure translated content?
  • E.g. do we add a language code to the content files (my-blog-post.en.mdx or anderer-blog-post.de.mdx) or do we use different folders (e.g. blog/my-first-post/en.mdx or blog/my-first-post/de.mdx)
  • Where do we store currently set language data (aka "What happens when someone clicks on the language switcher?"). Put it into a cookie? Or rather LocalStorage?
  • How do we handle routing/redirects, when someone looks at an english blogpost, he should be redirected to the German blogpost, when he clicks the language switcher. The German blogpost might have a different slug.