Yes, a person is responsible themselves for making sure they understand what they sign: they have the right to not sign a contract or enter into an agreement without having a translated version or without at least having an interpreter orally translate it for them. No one forced your colleague to sign: he chose to do so. Having chosen to sign the agreement, he is bound to its terms. He can try to dispute it in court (e.g. file a legal action for a "declaratory judgment" or court determination that the contract is void because of fraud and unilaterlal mistake--that they knowingly lied to him and the contract he signed is not what he thought it was; or he can wait to be sued and raise this as a defense) and he may be successful, but he needs to understand that the legal presumption is that you agree to what you signed, and the fact that he chose to sign without having the document translated will weigh heavily against him: he cannot actually say what was in the contract because he chose to sign without understanding it, and that will make it hard to show that he was defrauded, since fraud requires that the defrauded party have "reasonably" relied on the other party's representations--but there is not reasonable about signing something you can't read. His odds of winning are not necessarily good.