Actually you are entirely wrong. Language and Culture are dynamic and constantly evolving even without outside influence. 
What happens when 2 or more disparate groups become entangled, is a combination of language, culture and social mores. This process is effected by time, technology and external factors such as the awareness of changes in other societies without any direct entanglement.  Eventually a hybrid culture is adopted by most members of the entangled social groups and individuals discern only one notable group where there used to be several.

History shows that the overwhelming trend in cultural evolution is much like biological evolution. Only those cultural traits that are useful (improve the survival odds of the social group) will transfer to each successful hybrid. 

Resistance to change leads to destruction and assuming your own superior exceptionalism is complete folly.