I first posted this as a comment over at Conversion Diary because, well, I am
verbose long-winded strange. Regardless, it is definitely possible to become fluent in a foreign language without immersion (though immersion is still a good idea).
I started taking Spanish I at age 15 in the 10th grade, and I remember transliterating “¿Cómo estás?” in some vague form in my notebook because I had no idea what the teacher was saying. In other words, I knew nothing. Today, I am what is referred to as a “near native speaker” of Spanish. My academic Spanish is better than that of most native speakers, and I freak people out from time to time because I sound like I had been raised in Mexico City. What I did, starting out as soon as I could memorize the spellings of a few Spanish words was I would sign them to myself using the fingerspelling alphabet. The sheer repetition helped me memorize these initial words. After a year or two, I got into the habit of translating English conversations in my head while spelling out the Spanish words with my hand using the fingerspelling alphabet. I actually did this while continuing to talk with the other person. Strange, of course, but nevertheless effective. Again, more repetition. Really, a lot of repetition. Eventually, I got a job as a cook and started taking Spanish classes in college. I would eventually major in Modern Languages and Linguistics with a focus on Spanish literature. After a couple of years of college, I took 3 months of Spanish classes at Centro de Lenguaje America Latina language school, in Quetzaltenango, Guatemala, and then I studied for three semesters in Mexico City, where I met the woman who would be my wife and married her. When I tell the story, everyone thinks that my Spanish became good because I lived for so long in Mexico and married a Mexican woman, but the fact is my Spanish was good before I ever left the U.S. In Mexico, my usage became more fluid; my accent became Mexican; and my vocabulary greatly expanded.
On that note, the absolute best way to improve your language skills is to read in that language using two different approaches. The first is to read slowly, looking up words you do not know in a dictionary. The second is to read quickly without the dictionary, trying your best to figure out words from context. Either of these requires a bit of grammatical skill, but given the proper level of book, you can begin using both approaches early in language study. The key is to understand that there is a time and place for understanding everything with precision – that is why you use a dictionary in one approach – as well as a time and place for ignoring precision. The two together, engaged at separate times will help you greatly expand your vocabulary.
And a point of caution. Don’t fret about pronunciation. I mean ignore it if at all possible. You do need to study how words are pronounced, but focus on that only when you actually engage in that sort of study. At all other times, whether reading aloud or engaging in conversation with someone, try your best to ignore how strange you think you sound. The fact is no one cares that you sound strange. Everyone is, in fact, beaming that you are trying your best to learn. And fear of mispronunciation is, in my experience, the greatest impediment to actually learning a foreign language. The worst part is that there is no logical reason for this fear. It is a purely emotional response to how we perceive our own incompetence (as we think it to be). No one else sees incompetence. They only see someone who is trying hard.
There does seem to be a common thread throughout all the suggestions over at Conversion Diary. The first is repeat, repeat, repeat, and then repeat some more! Whether by watching telenovelas or fingerspelling Spanish words, the effect is to get Spanish coursing through your brain in a way that lets you remember. The second is practice, practice, practice. All that repetition will be reinforced even further if you ignore how badly you think you are speaking or listening or reading or writing, and simply set yourself to the task every day. To that, I would add read, read, read! Get some children’s books in Spanish. When you and your kids have mastered those, move on. And apply the slow-plus-dictionary and fast-sans-dictionary approaches to your reading at different times. You really need both to learn the language.
I guess the final recommendation would be to get a part-time job at a restaurant, where Spanish is often spoken. A bit of immersion is readily available in many parts of the U.S., so you might as well go after it.