Link Fallback for Localized Articles

[brycewc]

For those that don't have every page of their documentation translated into a different language, it can be quite taxing to have links across your documentation updated from the main language to the localized version once an article has beeen translated.

I propose adding a language fallback, such that an article in one language (e.g., Japanese) can have all of its links go to articles of the same language, whether they exist or not, and redirect to a fallback language (e.g., English) when one doesn't exist yet.

For example, the article /ja/overview has a link to /ja/apis which doesn't exist yet so it fallsback to /en/apis (or /apis) until /ja/apis exists, then it correctly goes to /ja/apis without the link in /ja/overview ever having to have been updated from /apis to /ja/apis.