The iRead4Skills project introduces an intelligent reading system to aid low-literacy adult native speakers by assessing text complexity and suggesting suitable readings. This report outlines our approach to understanding text complexity, reviewing existing frameworks, and developing our own. It's structured into key sections: Section 2 examines text complexity dimensions and assessment methods. Section 3 describes our guiding tools and frameworks. Section 4 details our methodology for defining complexity levels, including descriptors for French (FR), Portuguese (PT), and Spanish (SP), validated by Adult Learning (AL) and Vocational Educational Training (VET) experts. The report culminates with finalized complexity level descriptions for the iRead4Skills project.