It's not super common but if I was playing against somebody who didn't speak the lingua franca I'd probably throw out a couple phonies to test the waters.

The CSW is the official English word list used internationally (outside of the US/Thailand/Canada because we just HAD to be different) and contains over a quarter of a million words. Unless you're at the UPPER OF UPPER ECHELONS, there's a chance a crafty player could slip a phony in by hooking an "S" on the board or some other subtle stem - especially with the pressure of time controls.