It's not.
At first I was sort of scared that it might be, but then I realized that it wasn't like those really tricky questions of subjectivity like "is anyone except you self-aware?" Good luck answering that one, and even if you do, I won't believe you because you could be programmed to answer that way.
But answering this one only takes a digital camera with a timer: Digital because it's cooler, and with a timer so it's cleaner.
First I pulled the window shades down in the room. Then I shut the door. Then I activated the electromagnetic anti-Van Eck Phreaking array. I set the timer on my camera, pointed it at the screen, and ran out of the room.
Then I picked myself up off the floor and remembered that I had shut the door. A few seconds later, I was outside, and the room was all but invulnerable to spying. No one was watching that troublesome sentence of questionable Spanish. A timer expired, the digital camera emitted a digital click and an analog flash, and the hard part was over. I opened the door, lifted the shades, and shut off the humming array.
The sentence on the screen was still in English, and so was the one in the digital camera's digital memory. Therefore, it does not change when I am not looking.
Though come to think of it, I don't know Spanish. People who claimed to speak Spanish may only have been muttering random syllables to confuse me. How do I know that this so-called "Spanish" doesn't really look and sound exactly like English? Maybe it's just another liberal myth, or even a self-perpetuating lie. Maybe everyone who speaks "Spanish" thinks that he is the only one who is mumbling nonsense and has only managed to fool everyone else by dumb luck. Maybe no one wants to be the first to point out the reality of the Emperor's New Clothes. Sure, you'll tell me that it really exists, that it is a legitimate language, even that you yourself know it, but I think you're just unwilling to be the first to admit the terrible secret that you and all "Spanish"-speakers unwittingly share.
Never fear someone wearing a tin-foil hat: the real psychos weave the stuff into their thoughts. And never believe anyone who says they speak "Spanish."