International legal scholars debate fragmentation of international law as a possible effect of domestic courts' engagement with it. Among proposals to avoid fragmentation, scholars believe that using the VCLT is necessary for domestic courts to interpret international law “correctly”. This thesis contends that fragmentation depends on one's perspective on the nature of international law, proposing a linguistic approach to analyse it which distinguishes problems of coherence and consistency, a distinction that impacts on accountability for fragmentation. Analysing over 400 cases on GATT-related matters before Brazilian courts in the period between 2014-2018, and comparing national and international interpretations of the same legal rules, this thesis has not found a statistic relevant level of inconsistency. Although Brazilian courts never used the VCLT to interpret GATT, nor referred to WTO case law or WTO adjudicating bodies' interpretation, their interpretation of the same legal rules did not differ from that of WTO adjudicating bodies.