If little Joey wants IBM's high-powered Personal Computer/XT for Christmas, watch out. He may be scheming to cheat on his Spanish papers. Even if he gets away with it, he may wind up with a lousy grade.

Weidner Communications Corp. has come up with bilingual-translation software for the IBM PC/XT. Selling for $11,000, MicroCat 20 translates in one direction and takes about an hour to turn a 1,000-word English memo into Spanish including time for a human translator--who might take most of a day to do the job without a computer -- to clean up the copy. Weidner, of Northbrook, Ill., offers eight different translation packages, including English-to-Spanish.

To translate a sentence, the computer analyzes the grammar and looks up the words in a bilingual dictionary stored in the computer. Then it translates the sentence following rules of grammar from the second language. Weidner's MicroCat 20 software packages come with 12,000-entry dictionaries that are also expandable.

Weidner has sold more than 40 packages to such companies as Lockheed, Westinghouse Electric, and Toyota Canada, as well as to federal government agencies.

Computer translators can take things too literally, with funny results. Your warnings about Houston traffic jams may puzzle your Mexican supplier, who might receive a message about those dangerous new condiments, "jellies of traffic." MicroCat 20 is supposed to get at least 90% of the message right, enough for a good first draft. For the moment, anyway, human translators still have a place.