I would say "of course learning a new language will improve one's reading skills," if for no other reason than so many languages share etymological roots. When I started learning Russian in my forties, my understanding of many languages increased substantially. It also left me with an odd "tick" where I often read C with an S sound.
Language is more easily learned at a young age, but I would say it's never too late. Since learning new languages opens the door to new sources of information, it stands to reason this may increase language skills IQ metrics. Learning a new language will build new pathways into your brain, making for more adaptive thinking. You may not be able to form new grey matter, but the brain is constantly rewiring itself and building new adaptive pathways in the brain is a path toward greater overall function.
When I was learning Russian, even before I had a conscious understanding of the language I was already dreaming in Russian. Since it's been years since I had contact with my Russian peers, those language skills have all but passed. I'm sure it would be easier to pick it up again, but at this point I doubt I could carry on a conversation in Russian with a six year old.
All anecdotal, but it seems by your question you're considering the merit of trying to learn a new language, and to that I would say "Learn all you can." As a programmer, would you spend your entire career married to a single programming language? It would be very hard to function like that and, in this world we now live, I think it will be increasingly difficult to function at a high level without at least a basic understanding of several languages. It will definitely give you greater insight into language in general, and most likely into your own native language.
As to Russian in particular, I can say (and others agree) it's really pretty easy once you've mastered the Cyrillic alphabet.