What functionality is missing? What is unsatisfying with the current situation?

As a writer and user of WorldAnvil (WA) with a native language that is not English I still tend to write in my native language (Danish), since this is a language I am more comfortable with using and more proficient in. However, I find it is more difficult to get feedback or sufficiently be included in various challenges provided by the creators of WA.
I could of cause write all my content in English, but I feel that would limit me in my creation, and my usage of WA, since I am - not surprisingly - more proficient in my mother tongue.
Therefore I would suggest a translation system, in which each article will get a separate/parallel page, where the translated text and content would be accessible for non-native speakers of the language of the article.

How does this feature request address the current situation?

A translation page would help non-native English speakers connect with more people through a shared language, and be able to write in a language they are more proficient in, and still get worldwide feedback.
Imagine for each article you create there would be a button or symbol one could press and would provide you, the creator, with the ability to translate the article. This would not be a systematically generated or Google-Translate translation of the article, but a translation the author themselves would provide. For every given article it would be a possibility to create a parallel page, with the same setup and linking properties, like the one you are already working on - because the articles would be the same one!
When publishing an article readers would have the ability to shift between languages: the native language the article was original written in, and into the English version - or perhaps another language, though this is not the primary function or request of this feature. In this way, the same article would have larger accessibility, and a non-native English writer would be free to write in their native language, without losing access to feedback or feeling left out of the community.
In this way people, like myself, would not need to create a world-page and then feel the need to create a separate world-page, simply to write all the content again, but in English.   For similar translatable pages, one could look at Wikipedia, though not perfect, which provides the reader with the ability to shift between languages. Not to say the WA translation system should work the same way, however, the idea of a single article provided in multiple languages could be of high importance and value for sharing content across nations and countries.  

What are other uses for this feature request?

The main focus and feature of this request would be an in-article translation of content, where the translation would be provided by the creator themselves. It should still be possible not to translate an article if one so wishes, then the article would appear as normal with no possible 'translation option' visible.
However, for further investigation of the possibility of translated material and content, users of WA could help each other to further translate material into all sorts of languages.
World Builders and creators could help each other translate articles from one language to another to further share each other's worlds and creations. An article could contain multiple translations, from languages from English to Spanish, Mandarin to German, or even Finish.   A feature such as translation would make WA more accessible, relevant, and approachable for more writers cross-culturally. For the moment I find WA heavily catered to the more western English-speaking world, which is undoubtedly a shame due to the fact that WA is in my opinion the best worldbuilding site available - both for free and for payment. I enjoy, and will continue to enjoy using and creating with the tools provided by WA, it is a delight to work in, however, it would be much more helpful to me, and I can imagine other non-native English speakers if a translation option was added.