It's true that having error message in one's own language is really helpful but it should also be considered that having the same error message for everybody makes googling errors easier. It also give the possibility to people not knowing your language to understand what the error means and so to give you help. That's why error translation are often reserved to non technical matters that a standard user can solve easily or each error need to have a unique error code and a table where user helpers can find a translation but that adds complexity in bug reporting and reading.
