Building on the premises of the LETRINT project, this study shows the applicability of a corpus-based methodology to identify patterns of legal terminological decision-making and measure their quality according to translation adequacy requirements in international organizations. The comparative adequacy assessment of translations of five illustrative terms into French and Spanish in the main European Union institutions, the United Nations and the World Trade Organization broadens the scope of previous studies of terminology translation quality in this field. It provides empirical evidence of the correlations between legal term singularity, translation difficulty and adequacy levels, and also of the impact of intratextual inconsistencies on these levels. The approach and findings can be used to support translation quality assurance and terminological resource refinements.