What is the best way of filling in the meta information in a webshop with many different languages? Are the meta fields translated at the same way as the rest of the product- and custom pages? And if so, can Google and other search engines make it right when they show the webshop in the search result?

Yes they seem to be. My site shows the correct language strings when I search in google.fr , google.co.uk and google.es.
 
So enclose the meta information in the [xx]...[/xx] tags.