Many American Christians (usually in leadership or related roles) love to call foreign theological researchers to go back to their home countries (the reason given being to build their own countries), I think this is due to distrust or jealousy.
Distrust because they were afraid that the foreigners would want to "steal" their jobs in America. Jealousy because the reason for their distrust.
Nonetheless, I agree with the notion of taking what you've learned back home. However, the problem is identifying those foreigners who sincerely intend to do just that. If it is so, I don't think I need to call them out or remind them of their goals. Otherwise, unlike the Americans, I wouldn't even bother whether they stay or leave.
The reason I call these Americans hypocrites, is because they do not ask their missionaries to stay in other countries for good as much as they want the foreigners to leave theirs for good. Missionaries should live their calling, not treating it as a temporal phase of their lives. That would be vacation, showing off, risk toying, bride seeking, etc.