Make it more obvious that translations are available

Idea raised by @sorumfactory - are there ways we could make it obvious translations are available?

One way might be to [inspect the user's browser language preference](https://developer.mozilla.org/en-US/docs/Web/API/NavigatorLanguage/language) & to conditionally pop a modal.

Example flow:
1. User lands on https://launchpad.ethereum.org/en/checklist
2. App checks user's browser language, which is set to German
3. Pop modal, which explains the content is available in German, links to https://launchpad.ethereum.org/de/checklist (maybe https://launchpad.ethereum.org/en/languages as well?)
4. User can dismiss modal or click to view the site in German

Start by reviewing the /en/checklist and /de/checklist flows and the linked language page to understand how translated content is exposed. Then read the browser language preference guidance linked in the issue and investigate where a language suggestion could fit. Done means users whose browser language has an available translation can discover it, dismiss the suggestion, or follow the translated link.

Written by the indexing model from the issue text.