Generally people learn languages more quickly when they have already learned more than one such as is common in Europe. Most of our language skills are learned by age 6. attempting to learn a language later in life as a second language can be difficult for many people. Also it depends on whether or not the languages are similar in construction also. Russian, like Italian and Spanish genderize words and match them up and also have similar sentence structure, unlike English.
However, my point is that, if one wants to marry a Russian girl, I would think they would want to know all about her culture and history and family. This is infinitely easier the more Russian language the man knows. of course, one could simply say I don;t care about Russian and just want the woman and then there is a limit to the suitable candidates for marriage and also a loss of a wonderful culture.