This issue depends on which language are you referring.
In Argentina, Anglo-saxons, French and German inmigrants still keeps in good form their forefathers Language. I know 4th generation argentines descendants of England, Wales, Scotland, Ireland and France and Germany where they still speak those languages and of course Spanish, curiously with a slight foreign accent.
I my opinion, I think they are proud of their ancestor´s culture and they think that their culture is superior than the Mediterranean european countries. (Spain & Italy, i.e.)
I have just visited an estancia of French stock owners who before meals they pray in French. I warned them that I understand French as well, in a funny way, just to prevent any hidden criticism to me.
The main thing is the prestige of a Nation. This helps to keep the original language in good shape.
Spanish and Italian inmigrants do not think the same.
It is umcomfortable to me to say that from the XIX Century until now, Spain and Italy, mainly speaking, have had a poor performance in matters of technological issues, due that they arrived late to the Industrial Revolution.
No wonder that the mexican americans will forget their Spanish very quickly.
