In monitoring and evaluating the performance framework of the CAP, EU Member States are required to establish performance indicators (PI) that will ensure the evaluation of the performance and effectiveness of the main and specific objectives and priorities of each program. Inconsistent translation of EC regulations from English into Slovenian was observed in the context of the types of PI categories and their relations. There was inconsistency between regulations, ambiguity and uncertainty in certain parts of the regulations. This caused a violation of the principle of legal certainty for Slovenia towards the EU and the EC. It was found that legal translators in Slovene translations of some EC regulations use different terms for the same legal matter, which have a different meaning. This disrupts the hierarchical levels of the PI categories, which creates ambiguous obligations for Slovenia in parts of the regulation. The article presents EU and EC regulations, which clearly show the violation of the principle of legal certainty. Through the performed cognitive verbal semantic analysis and with the help of dictionaries, we propose appropriate translations of PI categories. We propose that the regulations and the official documents deriving from them be aligned with the next financial period 2021-2027.