The European Union as a political and economic project characterised by its supranational nature and cultural and linguistic diversity provides a broad research field for translation studies. The now 27 Member States speak with a single voice in every EU legislative act through 24 official EU languages, an achievement only possible because translation plays a key role in legislative procedure that requires an intense negotiation to attain versions of EU legislative texts equally authentic. Indeed, EU target texts as a genre conform to specific conventions and norms, and fulfil the expectation of the translation commissioner, i.e., the EU Institution commissioning the job. Furthermore, language contact through translation of EU legislation gives rise to standardised lexical variants known as Eurolects. Bearing this in mind and appealing to Even-Zohar and Toury’s framework to put EU translation in context, using a corpus linguistics approach, it is our aim to learn the influence of the Portuguese Eurolect on national legislative legal language through the specialised phraseology of environmental law between 1985 and 2019. This presentation will present the criteria selected to build a comparable corpus for this project. The corpus is composed of 405 directives (C1), the primary version of the Portuguese Eurolect and product of interlinguistic translation, 368 national implementing measures (C2), which result from transposition or rewriting, and disperse legislation without connection to the EU (C3). According to our knowledge, this is the first attempt to study the Eurolect phenomenon in the Portuguese language as part of an ongoing doctoral research project.