Going by the terms you remember, it wasn’t Forever War by Joe Haldeman, though the main character (named Mandela, naturally born in the 1970’s) eventually becomes a commander of a company of far-future infantry who were bred ex-utero in a selective fashion by the government (their last name being the gamete donor with the “higher genetic rating”). Homosexually is the enforced norm in human society at this point to allow the government to practice eugenics and have total control over population growth. They all need to be taught 20th century American English in order to be able to communicate with him! (Mandela has survived several campaigns and experienced much time dilation from relativistic travel between wormhole-like ‘collapsars’.) Mandela thinks back to his first company commander and tries to imagine how much more he would have hated him if he had been a sexual deviant by his standards and he also had to learn and speak a foreign language at all times for his convenience.