Language understanding in interpreting is inextricable for any interpreter.It is inextricable and essential for an interpreter to tackle this thorny problem on his or her way to a successful interpreting task.For interpreters,untranslatability or uncertainty in language understanding is nightmare.Philosophically,people are tortured by that I know where I-ache.I-ache is the support for private language.Private language is one thing that results in uncertainty in language understanding and uncertainty or untranslatability in interpreting.There is psychological basis or motivation to dissolve the problem.They are public language and mitsein.Public language is late Wittgenstein’s concept,while the latter comes from Heidegger.