One of the crucial elements for marriage is commuication.Communication by speaking and writing is very important when higher level of thinking is to be exchanged.Also,human being's cognative process is based on memory of past learning and experience,people of differnet life tracks may also be difficult to understand each other.Thus,I am pessimistic about the internal and eternal happiness of those involved in cross-country marriage.
The exception is that one part is willing to sacrifice by giving up his/her own culture and ceding to the culture and language of his/her loved ones.I do have one friend who seems to live a happy life,which I think is because his wife,a white lady,is willing to learn to speack Chinese,cook Chinese food,and behave like a tranditional Chinese lady (by quitting her job,staying at home,and give birth to 4 kids,etc.)