This might be an obvious point to many SEOs but Pierre Far from Google clarified that if you have specific landing pages for the same product but targeting different languages/countries, you can change the title tag of the page without concern.
Pierre Far from Google posted this on Google+ saying:
In my last webmaster office hours hangout I got an interesting question: When a webmaster uses rel-alternate-hreflang annotations to mark up a cluster of equivalent pages that target different language-country combinations, can the titles be different for each country?
The answer is yes, use a title that makes sense for your users and your site.
I go more into detail about how to handle these specialized annotations over here.
Pierre Far then gives some more examples of how this applies on Google+.
Forum discussion at Google+.