Christina, I am fully aware of all the differences between the different ways to speak Spanish (at school, here in Spain, you have to study Spanish Language and Literature for 12 years, and they teach us the most significant differences). But for a non Spanish speaking person trying to learn it to communicate with other people (not at scholar level) the differences are quite easy to spot and not very hard to learn. We understand each other, really :)
Yes , I used the word "slang", it's my fault(and my English ;) ). I didn't mean exactly that. You explained it much better. But pronunciation is different even between Spanish regions...so it is not regarded here as to make a difference impeding communication.

In response to Christina's post -- slang or no, I think the comparison between Latin American/European Spanish and British/American English is pretty dead-on. Some of the differences can be attributed to slang, some to different words for the same action, and some to accent (such as the pronunciation of the letter 'y'). So if you learn Spanish in Florida, you may have some trouble understanding it in Spain, because the language won't be familiar enough yet to understand it when it's spoken with a new accent.

Also, I think the best description I've heard for "fluent" is that you no longer translate the words to English in your head; you just understand them. I knew I was fluent when I started dreaming in Spanish. Eek!

As far as my comment that it might not help with communication in some areas of Spain, I should clarify that I was referring to some of the Basque regions like Cataluna that have their own language -- not to the differences in accent, slang, etc.

Jessie, I still think a working knowledge of any romance language will go a long way while traveling, even if you're not ready to teach college-level Spanish or French or Dutch when you get home. ;)

"think the comparison between Latin American/European Spanish and British/American English is pretty dead-on"

British English? There is more variety within Britain than there is between standard English and US English.

Now we're just splitting hairs. I meant, if you're American and speak English, you'll absolutely be able to understand people in the UK, even if you don't know what trainers are or what chavvy means. That's all. There are plenty of variations within the US, too, all of which are also fairly irrelevant.

When the film Trainspotting came out in the US they put English subtitles on it so that americans could understand (the Glaswegian.)

If you learned spanish and went to S.America, it would be inicially tricky to understand as you tune into the vowel sounds. then you would get used to it.
this applies to regional accents
around Spain as well- some are more textbook than others.
That said, the Spanish you learn and the Spanish you speak day-to-day are two different things and can only be picked up from talking and listening and copying.

For a trip through Italy, Spain, Monaco, and Amsterdam, French would be the most useful language (after English).

It takes about 800 hours of study to become fluent in a language from the same family, so learning any Western European language for an English speaker would require about three months of <i>full-time</i> student. If you are doing it only an hour or two a week, it will take years.

In any case, since you already speak English, there really isn't any point in learning any other language, as you won't become usefully fluent quickly enough, and there will be lots of people in all the countries you visit who speak English.