I'm moving this to Touring, but here are my two cents.
I don't mean to discourage you, but many areas in Central/South America are very difficult to ride across either physically, safely or both. With this, I highly recommend talking to others that have done a route similar to this.
As far as language requirements go, you will probably be okay in the larger cities if your Spanish is rusty. However, most of the smaller cities do not know a word of English and may even use more difficult Spanish dialects. Therefore, I agree with others in that having a very fluent understanding of the language will be essential in making your ride a lot easier.
I hope this helps, though I haven't done cross-country cycling like this before.
__________________
Ride more.
Code:
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