What if a person is illiterate in English?  If they only speak Spanish or Yiddish or Russian?  They can read and write in their own language but not in English.  Is the contract still valid?  Generally, assuming the person is mentally competent, they have a responsibility to learn what they are signing.  That means that it is their responsibility to get someone to translate the contract.  But in a retail setting the illiterate may have an argument that the contract is unconscionable.  A great deal will depend on the facts however and exactly what the contract was for.    It will also depend on who did the translating.  Advice for the businessperson:  have the contract translated if you can.  If not, have them bring a translator because you, the business owner, don’t want to be in the position of “Well, he told me that it was OK before I signed the contract.”