Improve: If the page has no translation, set the English version

[FranciscoJBrito]

Description

I see that some pages are missing in the Spanish version, currently it shows the 404 page. I think it is a better option to set the English version if the translation is not finished. This allows you to continue reading without problems. As an additional detail, a notice could be added at the top of the page, saying that the translation is still being worked on.

---