Thanks for this report - we will look into it! In the meantime, I seem to be able to access other pages by entering the desired language code directly into my browser's address bar - e.g. https://www.accesstomemory.org/de/
Keep in mind that unfortunately, we still haven't yet been able to add the necessary infrastructure to translate the documentation itself. Switching the language of the AtoM website will update any homepage content and navigational tabs that have been translated, but not the documentation content. This remains something we hope to improve upon in the future.