According to many listing of movie clichés, one of the most commonly used is what I have taken to calling The Speedy Gonzales Syndrome.  It is the inability of foreign persons to remember or use common short words in the english language such as "yes", "no", "please", etc, even when they are capable of forming complete sentences, sometimes with proper grammar.

For example: "that gringo pussycat is mucho loco" (from Speedy Gonzales), "Glotis, are you loco" (from Grim Fandango), "Bender, think of the señoritas" (from Futurama).

This is not by any means limited to spanish.  French, russian (usually limited to nyet and da) and other languages are also commonly present in this situations.

Ok, so by definition it is not probably a syndrome, but what do I know.

enkidu has pointed to me that sometimes the words are rendered in the speaker's native tonge in order to place emphasis. This is, of course, true. and in fact the Futurama example is out of place in this writeup since Fry's use of the word señorita was because Bender had previously remarked that he was mexican (while opening his chest and showing a sign that read "Hecho en Mexico").

The Speedy Gonzales syndrome is about the gratuitous use of foreign words while saying english sentences. One of the characteristics of this words is that they are usually "common knowledge" in english (si, no, gracias, oui), hence the note on use of the russian language above.