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I've used the tool on a single domain in a shop environment, unfortunately I've seen little to no effect. I did notice however that Google's tool is relatively poor at picking up it's own highlights once set. This may just be my personal experience with the tool though.

I have on the other hand used schema mark-up on another eCommerce site and seen not only improved CTR, but the SERP results returned have tended to be more accurate and useful (in my eyes) for customers/potential customers.

This is a response to both questions. Rel = canonical will give in this case the English page the authority, that should be the page that ranks well.

The main issue here is if the whole page is translated don't use a canonical tag, if the content stays in English and the Navigation/footer is changed use canonical tag to the English page as this would verge on duplicate content.