Use a browser's "translate" feature on a page where we list languages in their local names and be amused how the browser bungles the translation. Or use a screen reader to let it read out the language names and be amused that it pronounces everything in an English accent.
The solution is to add a lang-attribute to the DOM element containing the localised language name to let the browser know what language this is in. So for the German language entry, the attribute should be lang="de" for example.
We have these language lists in several places.
The language dropdown in the "Post New" form: https://test.archiveofourown.org/works/new
The language selection in the browse filters: https://test.archiveofourown.org/tags/1*s*2%20Wangzi%20%7C%201*s*2%20Prince/works
Our list of supported languages: https://test.archiveofourown.org/languages
Language filters for the admin posts: https://test.archiveofourown.org/admin_posts
Posting form for admin posts https://test.ao3.org/admin_posts/new
List of locales: https://test.archiveofourown.org/locales
Language drop down on the new locale page: https://test.archiveofourown.org/locales/new
The Abuse form: https://test.archiveofourown.org/abuse_reports/new
The Support form and page text: https://test.ao3.org/support
Preferences page for any accounts where the "Your locale" option is enabled via rollout (which should be all accounts on dev/staging, I think): https://test.archiveofourown.org/users/USERNAME/preferences
Work search: http://test.ao3.org/works/search
FAQ filters: https://test.archiveofourown.org/faq
This may not be a complete list.