Hmm..never ever thought how it would be to speak only one language. I've been atleast biligual most my life if not triligual. No big deal for a lot of people. I picked up English from sesame street even before I started K.G
At the moment I can speak, English, Urdu/Hindi ( almost the same thing ) Arabic, Punjabi, some basic Phusto and very crude German and trying to learn my what my wife speaks ! Tagalo !!!! and some malyalam ( have to speak that to survive in UAE) Since Mallus are the majoritiy here
Oh and I can curse in about a million languages
But thats nothing I know a dude know who works as a desert tour guide for Orient tours. Totally illiterate. Along with the common UAE languages of English, Arabic, Urdu and some native blah blah, Speaks Fluent German, Russian and Spanish now thats awesome.
I personally think the key to getting it right is to get the accent down correctly. You can get away with a minimal vocabulary if you have the accent right. But even with good vocabulary and a bad accent it gives the impression the speaker is not really fluent in that language.