[...] Allow me to share some autobiographical details, perhaps relevant to our discussion of language and diplomacy: I had the good fortune of growing up essentially bilingual; my father, an FSO [Foreign Service Officer], was posted in France and Belgium, and French is my "native" language. I attended local French-speaking schools in these two countries; for the fifth grade, my parents, deciding that, as an American, I should after all speak English, sent me a to an "international," English-speaking school in Brussels, where I acquired English (with which I still have problems with prepositions, among many others). But to my main point: I fully agree with you that "learning a language properly does take a lifetime" -- not a "language training" stint at (God bless the organization) at FSI [Foreign Service Institute, which "trains" USA diplomats, including in foreign languages].
My agreement with your wise statement on learning a language [it requires a lifetime] is based on the experience I had of speaking French as a child, and being thus very sensitive (even until now) to the negative impression made by Americans, after a "quickie" language course, that they are capable of "parler français." I should note -- although my struggle with Russian will never end [although I have studied it since high school] -- that official Americans who don't have full Russian fluency addressing Russian audiences on Facebook/Twitter messages with ungrammatical Russian are not automatically well received, especially if they extend their remarks beyond a few polite words in their "Russian."
I witnessed how Russians cringed at Americans speaking Russian (including myself) all too often during my years in Moscow (98-01).