As explained on the Relationships, Social Environment and Social Network Optimization websites, the quality of matches between people depends on the size of the pool of candidates from whom the individuals are chosen. International borders and residence requirements limit pool size, but linguistic barriers are often more constraining.
When China claimed Tibet as its territory, the Tibetan-Chinese border ceased to be a problem limiting relationships between individuals in the two areas. But the Tibetan and Mandarin Chinese are entirely different languages from different language families. That difference serves as an even greater barrier than the border ever did.
Bilingualism will eventually solve that problem, as more and more people in Tibet learn Mandarin. But then the Tibetan language will be threatened, and in danger of becoming extinct.
The problems and opportunities are shown by the numbers. Approximately 1.2 million people speak Standard Tibetan. Over a billion people speak one or another dialect of Chinese, with over 830 million speaking Mandarin as a native tongue and over 900 million fluent in the dialect. If all of the 1.2 million speakers of Tibetan learned Mandarin Chinese as a second language, they would join pool of almost a billion people who could use that language in interpersonal relationships.
A very crude estimate is that 5 to 10 percent of the Asian population marries each year. That would be perhaps 100 thousand Tibetans and 100 million Mandarin speakers.
As an even cruder estimate, a speaker of Tibetan would at most be able to choose among the best 50 thousand possible spouses. A speaker of Mandarin Chinese would be able to choose from among 50 million possible spouses.
As a matter of choosing the most compatible person to marry, a Tibetan who learns Mandarin Chinese increases their pool of candidates by a factor of a thousand.
But if every Tibetan of marriageable age took advantage of that increased pool size, the Tibetan language and culture would almost disappear in two generations.
This is the language problem.
Solution? There seems to be only one, and that involves the controversial and often unpleasant approach of making something compulsory. Most countries make some studies of the native language or languages compulsory in schools. To solve the problem of global communication while preserving national language, it seems that education in at least two languages should be compulsory for at least a few years of childhood. One would be the most prominent national language, the other some agreed upon international language. It seems that the world is heading in the direction of having English as that international language. It is, for example, the official international language of aviation.
There are many problems with having the language of one or a few nations becoming a true international language. English would not be a good choice anyway, being highly idiomatic and arbitrary, full of historical artifacts. An alternative is a constructed language. My own proposal for one is to be found on my acronymic languages site.