I have a website where every page (http://www.example.com) has a separate mobile version (http://m.example.com). And I simply use the rel="canonical" tag on one of those two pages to avoid duplicate content issues with the search engines.
Now I am adding other language versions to the same website as subdirectories (http://www.example.com/fr/ for French version). The translated pages will also each have a separate mobile version (http://m.example.com/fr/).
I know that the rel="alternate" tag needs to be included on all existing pages to tell the search engines that these are just different language versions of the same page.
My question is: On which pages should I include the rel="canonical" tag? For example, if I do not include the canonical tag in one of the two French versions of a page, wouldn't search engines see the French mobile and non-mobile versions of a page as duplicate content?
And if I do include the canonical tag in one of the French pages, would that not create duplicate content issues again - because now the original language version (http://www.example.com) and the French version (http://www.example.com/fr/) of the same text both have canonical tags in them?
Or would the rel="alternate" tag linking the original language version of a page and its translated version make sure that both of these pages having canonical tags is not a duplicate content issue?