Since the URL is changing and we have to do a 301 redirect anyway, why not change it to something unique like en.war2.ru? (Or war2.ru/en/, doesn't really matter.) That would prevent potential confusion between the two very similar URLs, and it's still transparent for users because of 301 redirect from server.war2.ru to the new URL. As long as you do the 301 redirect Google will pick up on the change and replace server.war2.ru in SERPs with the new URL either way.