In this paper we report on our analysis of multilinguality support for thesauri, with special reference to the AGROVOC thesaurus. We highlight that AGROVOC makes exclusive use of ISO 639 to tag languages, and we comment of its appropriateness for a resource such as AGROVOC. We provide examples taken from the subject area of AGROVOC to show the many cases of loan-words that appear when talking about plants and foods in different geographical areas even within countries speaking the same language. Our work is widely based on the Spanish and Portuguese cases