I experienced language barriers on different levels after I moved to Zurich.
First of all, I don't speak Swiss German, and I only know a little bit of standard German. I've been here for three months now, and I realized that unless I learn the language, I won't fully participate in life of this country. I might as well live in China, Iraq, or Bolivia: not likely to really get to know many Swiss. I won't really experience cultural events. I won't even be able to chat with randomly met people, because it's rather awkward to start a conversation in English when you don't know if the other person speaks it. Sure, a lot of Swiss do. But it's much easier to approach other people if I speak their native language. Not expecting anyone to learn Polish either!
As a colleague put it, there are several social "bubbles" around me I can try to get into: Polish community, various English-speaking communities, colleagues and perhaps their families/friends. Actual Swiss bubble is likely to be the most difficult one to fit into: between them it's more natural to speak German. Even when I'm among them they'll often switch to their native language from time to time, effectively excluding me from conversation. Not very polite, I could do something to stop it, but what if I didn't really need to?!
Here's an example. I was playing in a small poker tournament for casual players in a local pub the other day. I was the only foreigner at the table. Live poker is currently one of my favorite games, but turns out that chatting is a hugely important component of it. And the same thing happened - when addressing me (rarely), the other players would speak English; otherwise, they mostly used Swiss German. The evening lost its appeal completely when all that was left was cards.
I also visited United States twice over the past quarter. I could approach anyone and simply chat with them, be it someone at work or someone on the street. Americans I met seemed to love to chat with strangers. But what really struck me was how easy it was to fit in. Whenever a conversation was taking place, I was able to participate. A wonderful feeling. It would be great to experience it in every country I visit.
Before coming here I wasn't sure if I'm going to learn German. Now I'm much more motivated.
The other kinds of problems are more subtle, and they're related to English which is my only strong foreign language. I can talk, read and write it with ease; it's uncommon for me to hear a word or phrase in a conversation that I hadn't heard before. And even though I've been learning English since I was 8, at times it's still not good enough. Two frequent problems I'm facing are: not hearing well enough from a distance, and not being able to express my thoughts when surprised or stressed.
Let's suppose I'm eating lunch with a bunch of colleagues. We chat. Sometimes I just can't pick up words, phrases, even complete sentences. I don't think it's hearing impairment. If it was Polish, my "hearing radius" would be greatly extended. I also don't think that it's "not enough experience" -- in my life I heard thousands of hours of English, spoken by dozens of nationalities, and when speaking with the same people directly I don't have any problems with understanding. I seem to have difficulty in picking up words when there's some background noise and the speaker is a bit further away than usual, not talking directly to me.
The other problem can hit hard when I'm under pressure. Someone might have said something surprising, or I'm stressed for some reason. In situations like this I usually know what I want to say, but often find it difficult to recall the right words. I usually do say something, using whatever synonyms I can come up with quickly, but that doesn't express what I really meant. It's frustrating, often embarrassing. It seems that when I'm pressured, using foreign language is much more difficult. Not sure if it's a matter of language skill. It feels like my memory is impaired by the stress; maybe my organism reacts as if it was in danger which makes it focus on other things than speech.
The last issue is active vocabulary. It's not as annoying, I wouldn't even call it a problem, but it certainly is something I could improve. Knowing what a word means when I see it is easy. Being able to recall a word on my own when I need is another story. I'd pay a lot to artificially expand my active vocabulary to cover every word I know (implant, training, whatever). I think the freedom of speech I would gain that way would be truly liberating.
I'm not comparing the issues of not speaking a language (German in this case) and having minor difficulties in some situations with another one I'm fluent in. But significant conversational exposure uncovers those issues instantly, while just reading something on the Internet is really piece of cake. If you want to know what language skills you're actually lacking, I think the way to do so is not through taking courses but by going abroad into a country where it's the main spoken language. A couple of weeks and you'll know.
When I was a kid, I was always told by my mom that speaking foreign languages is very important in life. Once I mastered English (or rather once I thought I had mastered it), I became reluctant to invest time and effort into any other language. It seemed to me as though English is all that I would ever need, both in personal and professional life. Books, Internet, movies -- all the important resources are published in English eventually. English already is the international language, so why would I learn anything else?
Now I'm starting to think that speaking 3 additional foreign languages might be a life changer, an incredibly positive experience. As a European I'd probably start with Spanish, French and German. I already learned a bit of the last two in the past. It will take a lot of time to master them, but that's an investment risk I'm seriously considering taking.