[Plugin: WordPress SEO by Yoast] Sitemap generator is not language-specific

I am working currently on a multi-language website for which I am using WPML and WordPress SEO by Yoast. WordPress SEO plugin works really great for multiple languages except for some issue that does, however, bother me. When WordPress SEO generates XML sitemap, it mixes pages in all languages together when one would expect it to generate a separate set of XML files for each language.

Because I am using a separate domain per language, I end up with a sitemap that mixes pages from two domains. I do not know for sure but I assume Google does not like it at all.

From wpml.org forums I know that WordPress SEO by Yoast is in general very WPML-frienly and this issue is one of the minor things that are not perfect. WPML people are aware of the situation and aprox. 5 months ago there was a note from WMPL developer saying that

We need to work with Yoast so that WPML can communicate better with his SEO plugin. Right now, the SEO plugin dumps all the URLs in the same file, without knowing that some of them go to a different domain.

I do not know if there is any work in progress on that, but being a PHP developer I would like to offer Joost some of my time I’m willing to contribute in resolving this issue, if that be of any use.

In case this not work I am wondering if there are any other XML sitempag generators that are able to generate sitemap correctly (i.e. to have a separate sitemap per language) with WPML being used to handle different languages?

Best regards,
Kirill