This is an old question, but still relevant I think, and I just came across it today.
Do courses in Spanish speaking countries expect some knowledge of English as a prerequisite?
Most other answers here say you don't need to know English as a prerequisite. Although I'm sure it varies widely from university to university, at my university, UNED in Spain, they do expect you to have some level of English. Here it says
Es deseable un nivel básico/intermedio del idioma inglés. Especialmente la comprensión lectora del inglés permitirá el manejo de la abundante bibliografía existente en esta lengua. El alumno podrá encontrar algunas asignaturas con libros en inglés.
I had a couple classes where the textbook was in English. And on more than one occasion a professor gave additional material, or what have you, in English and the students were expected to be able to comprehend it. As a native English speaker, I had no problem with it, but there were others who complained about it.
Do they teach you what English keywords mean?
In my experience they do not teach you what the keywords mean, but rather how to use them. However, most are basic enough to look up in a dictionary and have a good understanding.
Are you taught to use English names for variables, classes, methods etc or Spanish ones (Confusing?!)?
We weren't really taught anything in regard to this. I'd say most just used Spanish for variable names, classes, methods, and for comments. I used English variables, classes, and methods, but comments in Spanish (for school work). I did ask my professors on a couple of times, and they usually all said that the way I did it was fine and probably preferred, since you'll find English in the "real world" more often than programs written in Spanish. I just find it easier and more natural to use English for variables, classes, and methods because all the other keywords are English. Also you come across issues like pluralizing variables and other things that I can't remember right know where English seems a little more convenient.
Lastly, can you get/do you use, things like Javadocs in Spanish?
Not sure if you can get it in Spanish. However, my recommendation would be to use the English. Even if you're not comfortable in English at first, force yourself. A lot of the same words and phrases are reused in lots of different situations, and pretty soon you'll find it easier. Then you'll have the added benefit of access to all the tutorials and example in English, which is a pretty big deal.