[11ty] defaultLanguage fallback for locale_url

[vwochnik]

Hello! Please forgive me if the issue already exists.

I have a project where I use the official I18n plugin. However, not all pages are translated to all languages. That means locale_url is throwing an Exception if a page with the current language derived from page.lang does not exist.

What I want locale_url to do is if it doesn't find a page with the current language it should fall back to the page of the default language.