How to know how many translations remains to make for bounty?

^^^

You appear to not have read the rules. Project:Rally-2012-12 states you need to make 500 new translations for specified products. On Special:Rally500 you can check if you have done so.

Really? What makes you think I have never read the rules?

Because the answer to your question is in the rules section.

"new translations for eligible products on translatewiki.net" doesn't really look like a link to page where you can see your stats, so it's not indicator of my knowledge of the rules :v