I see your point. But, I personally would be feel better under most all circumstances having at least rudimentary skills.
I'm pretty sure also when the soldiers said they would have to speak english. You would have to know more spanish than counting to ten. For them not to still have to speak to you in english to understand each other.
Also, AS long a you aren't carrying drugs or guns I would assume even the army wouldn't have a problem. And the easist way to avoid a search is to eagerly allow a search, IMO. Which is easy to do when you have nothing to hide. TRust me I'm against un substaniated searching more than any one, but you have to do what you have to do.
And if they were going to steal money or your bike or assault you, not understanding the language would be in consequential.
PLus, talking the least possible is a good idea with customs and law enforcement any where.
At the very least if I played dumb I'd like to know at least what they are saying.