This paper explores how the legal functions of international organizations condition the scope and properties of translation-mediated multilingualism as implemented in three representative settings: the European Union, the United Nations and the World Trade Organization. To this end, a multi-method interdisciplinary approach is applied encompassing various analyses of institutional text corpora, legal instruments, language policy documents and interviews with translation service managers. The data obtained provide evidence of the interconnection and variations of underlying legal, textual and linguistic hierarchies, together with pragmatic and political factors, as reflected in translation directionality, strategies and quality assurance, and in multilingual text interpretation. It is argued that these aspects serve to reveal the “depth” of institutional multilingualism beyond the “breadth” of language coverage.