Resolving conflicts with language subfolder and langage param - .htaccess

Question

On a multilingual joomla website, i have virtual subfolders for each langage, like this :
example.com/en/category/page
example.com/de/category/page
example.com/fr/category/page
But, in Google Webmaster Tools, i have 404 when it crawl on this :
example.com/en/category/page?lang=de
example.com/de/category/page?lang=fr
etc.
I tried this :
RewriteRule ^en/mypage$ http://www.example.com/en/mypage? [L,R=301]
But of course it make looping redirection that doesn't work.
How can I solve this kind of problem?
Is there a way to replace the langage param to always get something like this :
example.com/en/category/page?lang=en

Answer 1

If I understand your question correctly, then one solution would be to change your site map. This is how I usually do it on my multilingual Joomla sites.
1 - Install Xmap
2 - From the Joomla backend > Xmap, I create a new site map and under the menu option, I include all the menu links I want to be indexed, in all languages
3 - After publishing and saving, note the Xmap ID for this new site map.
4 - Create a new text file, similar to below. Save this to the root of your website as sitemap.xml
Note that you may need to change the xmap id to mantch 3 above, and you will need to add a <loc> entry for each language on your site
<?xml version="1.0" encoding="UTF-8"?>
<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
<sitemap>
<loc>http://your_domain/index.php?option=com_xmap&view=xml&id=1&lang=en</loc>
</sitemap>
<sitemap>
<loc>http://your_domain/index.php?option=com_xmap&view=xml&id=1&lang=fr</loc>
</sitemap>
</sitemapindex>
5 - Check that you can now reach the sitemaps for each language directly using the URLs from your <loc> lines above, e.g.:
http://your_domain/index.php?option=com_xmap&view=xml&id=1&lang=en
6 - Submit http://your_domain/sitemap.xml to Webmaster tools as the location of your site map. Google is smart enough to fgure out the language settings after that.
Good luck!

Answer 2

It's a little late but here the solution i used (David's answer was a very good start).
Xmap didn't exist anymore, and OSmap isn't the best solution because it doesn't follow the Google recommandations for multilingual sitemaps, wich says that it needs <xhtml:link rel="alternate"[...] for each links.
So : I used OSmap to get all links quiclky; then I manually create a properly formatted sitemap. Then I posted my sitemaps to webmaster tools (I got one for each language), and i place a sitemap_index.xml to help crawlers to find them.