It's a candidate for autocorrection -- shlal to shall, hte to the, tounge to tongue.  (Of course, unless a reviewer types his review in Word and then pastes it in here, autocorrection isn't available.) The frequency of the misspelling is probaby due to a combination of typographical errors by those who know how to spell the word; misspelling by those who have no idea how to spell the word; and jittery typing by those whose oxygenated blood supply is being diverted to their nether regions, thus depriving their brain of the stuff.

There's an asian toy called, "Tounge of Frog," in which the word tongue is mispelled.  These products often contain mispellings and broken english.  This is where you'll get any hits on most search engines.

If you are posting this to ridicule poor spelling in TER reviews, then you might want to review the grammar in your phrase "Is this a slang?"... I think you meant to say "Is this slang" or "Is this a slang term".

Try playing Neverwinter Nights online sometime and see how many people play a "rouge" in lieu of a "rogue". There is just something about the -gue ending that confounds spelling.

O.