Hi
GTranslate uses no plugin, is only a module.
That's not possible: if it's only a module, it can only work with javascript (unless maybe if they add stuff to your .htaccess). In that case, 4SEO will never see the translation.
As they also seem to be able to translate for a regular request, this would require a plugin.
is it not bad for SEO not having these links in the sitemap?
It's always best but if your pages are indexed despite the GTranslate mechanism, you do not seem to have a problem there. Until there's more information about why the pages are not discovered, whether GTranslate is only a module or not, etc, there's not much that can be done on our side.
Then another question: My problem is to choose in phoca cart a canonical link since the same products are in different categories.
Do you intend to do that as you have already done for virtuemart and hikashop?
I have not done anything for Virtuemart, only Hikashop has some support and it actually does this automatically itself anyway. Which is what Phoca Cart should do to be honest.
Providing this for Phocacart might happen in the future but it won't happen quickly. I think you'd be better off just asking for it with the Phoca team. For them it's really easy to do and would be good for them to have this as it's a basic SEO feature. They can add it in a few minutes for sure.
It may be possible for you to extend 4SEO using one of the hooks that are built into it. If Phoca does not provide a valid answer, please open a separate ticket for it. I cannot provide custom programming assistance, but it should be rather doable.
Best regards
Yannick Gaultier
weeblr.com / @weeblr