Klaatu says...?

Since it's only a three word phrase and Klaatu's name is one of them, it certainly would make sense if the writer had that in mind.

Whatever the message, "Klatuu" being the first word means that the next two words are a request from Klaatu.

The second and third words might be "says abort" to an attack which could have been a pre-planned response if Klaatu was captured and killed (a likely earth type response actually). So a simple interpretation might be: "Klaatu says abort".

What [deleted] said makes sense -- considering that when humans make up "alien" languages, they sometimes mimic known languages in their vocabulary and/or structure. Just offhand, I can think of several reasons why this may be so: 1) It never occurs to them that an unknown language would be different (this particularly applies to structure and phonemes, I suspect); 2) They assume the audience won't accept a language that sounds too different from what they're used to; 3) It may be an in-joke; and/or 4) It may be sheer coincidence.

Not meaning to imply that any of those reasons would apply to actual extra-terrestrial languages -- only to languages made up by humans, such as for films.

OP makes sense. Plausible, but we'll never know.