=== Background
It is possible to create pages and sections with preloaded text, using the [[ https://www.mediawiki.org/wiki/Manual:Creating_pages_with_preloaded_text | preload ]] URL parameter.
When a translateable page is the target of the `preload` param, it would be helpful to fall back to an appropriate language if a particular translation does not exist. For an example of where we might want to do this, see T296272#7619882.
We can do this using Special:MyLanguage, which redirects to a translated version of a given page in the user's language, using the [[ https://www.mediawiki.org/wiki/Manual:Language#Fallback_languages | fallback chain ]] if a translation is missing in that language.
=== Acceptance criteria
* When the target of the `preload` param is a translateable page for a language that does not yet have a translation, the page for the next available language in the fallback chain is preloaded instead. This should work for `action=edit` and `veaction=edit`