<p>I think it will be easy for your son to learn another language in addition to Russian, and I would encourage him to do so. He already has more sounds (phonemes) than English-only speakers as well as knowledge of other grammatical rules, concept of gendered nouns, and word roots. He would probably have no trouble with Spanish pronunciation, for example, due to some similarities in vowels, softened sounds, etc. My first language was Ukrainian and I took what I thought would be the easy way out and studied Russian in high school and minored in it in college. Needless to say, it was not as easy as I expected! I have no regrets but I wish I knew a Romance language too. (I started college Russian at 5th semester level freshman year. That is how I could minor in addition to a science major.)</p>
<p>In grad school I tried to become exempt from the language requirement which was at the time German! It was a Chemistry program, and a lot of older chemistry literature is only in German. They said Russian would not count, yet faculty would occasionally ask me to translate Russian articles for them! The injustice! I never learned German because they added computer language as an option to fulfill the requirement.</p>