'We have the right to talk and think in our own language.' This self-evident slogan is ever challenged in the digital age of the 21st century. 'Talking and thinking' is most effectively trained and achieved by formal education carried out in one's own language. However, multilingual children growing up in multilingual societies would have to adjust their own language to a language of education in schooling. This paper clarifies scientific grounds that in such situations the main root of learning and thinking through language is discontinuous. It is claimed that the students may face semilingualism, defined as 'linguistic competence insufficiently developed for complex conceptual thinking'. Multilingualism and semilingualism are two sides of one coin, and semilingualism is affecting many parts of the world. This is due to the established eminence of English as a global lingua franca (ELF), which serves as their language of education. This paper is qualitative in nature, pointing out discrepancies between the politically empowered unipolar concentration of English and cognitively suited languages for sustainable development of conceptual thinking. It is intended to serve as a reference point for educators and professionals who are responsible for raising human resources in the digitalized global age. [For the complete proceedings, see ED608557.]