I've experienced the same issue over the last year and a half. You can manually correct your sitemap by deleting a major portion (almost all) of it from the middle http://www.concrete5.org/marketplace/addons/internationalization/fo...
the multilingual sitemap process seems to restart the page list from start to finish for each parent page as its added, resulting in the huge number of duplicate listings you're experiencing.
I'm embarrassed to admit I was going to look for or develop a solution over a year ago and have just been manually updating instead :(
Has anyone else finished a working patch for this?

Adrian
Arvixe Web Hosting / Concrete5 Community Liaison |
http://www.arvixe.com/concrete5_hosting.................

Thanks for the response Adrian. It's good to know that there is a (manual) solution.

Unfortunately, with the advent of 5.7 who knows whether this bug will be officially solved. Remains to be seen...

Cheers,
Neal

I think this is a bug in the Internationalization (multilingual) add-on rather than the core if I understand this properly.

This was already fixed in the git repo of the add-on last year by @hissy:
https://github.com/concrete5/addon_internationalization/commit/51fbe...

Unfortunately it seems that this change never got its way to the marketplace version of the add-on... I can still see the bug in the latest downloadable release (1.3).

But you can fix it by following the code line change in the commit that I linked above.

EDIT: You can also always use the version available at the git repo.