[FEAT] Wildcard for language in multilanguage sitemap patterns

[SalahAdDin]

Feature request

Summary

We suggest adding a wildcard for languages in the sitemap URL patterns configuration.

Why is it needed?

Maybe it is not clear in the documentation, but now we can either create a global or language-per-language pattern.

In case we choose the global pattern it will be like: ``/en/posts/[slug]whereen` is the default language.

Using a wildcard/field on the pattern gives an issue now:

The other alternative is stating parameter language by language, but if the site has more than five languages, it will become a big annoying issue.

Suggested solution(s)

So, either making it clear in the documentation or enabling the [lang] field to be used as a wildcard will improve a lot the developer experience with this wonderful plugin.

Related issue(s)/PR(s)

Let us know if this is related to any issue/pull request.