Traditional negotiation systems have been implemented using agent architectures, where agents communicate exchanging negotiation primitives generated by each system, based on particular language definitions implicitly encoded, giving different syntax and semantics to their messages. In this paper we address the problem of communicating heterogeneous negotiation agents in a Web-based environment, considering differences in their language implementations. Our research is based in the development of an ontology solution for describing and sharing negotiation primitives; and a translator module which is executed only when a notUnderstood event occurs. We executed experiments in an electronic marketplace architecture, where heterogeneous agents participate in negotiation processes. The results of experiments show that the proposed solution improves the communication between negotiation agents.