The existing research on onomastics does not sufficiently reflect upon the relation between cultural codes and demonyms, having in mind that demonyms universally represent linguistic devices for expressing territorial and regional identity. The article focuses on the complex polyparadigmal analysis of the system of demonyms related to the macrotoponymy of the four founding countries of the Pacific Alliance: Chile, Colombia, Mexico, and Peru. Each of the four founding countries of the Pacific Alliance is characterised by the uniqueness of its culture, historical development, the specifics of the national variant of Spanish that reflects the indigenous influence of substrates and the collective values of the society. The research tasks of the article consist in systemising the morphological devices and the cultural layers of demonyms connected with the administrative division of given countries, detecting the variation parameters, comparing them from the linguacultural point of view. The main material of the research have been 100 official demonyms of Chile, Colombia, Mexico and Peru, and 31 variative denominations. The materials for the research are based on the official websites of the administrative units of the four countries, dictionaries data, diverse types of texts and discourse, as well as the notes of the informants speech. The research uses such methods as the continuous sampling method based on Internet sources, the analysis of dictionary definitions, the method of semantic interpretation, the morphological analysis, combined with interviews with informants whose interaction is made possible by the complex polyparadigmal analysis of the material. The authors have determined a series of lexemes that function as demonyms, analysed their form and content from the linguistic point of view. It has been revealed that the main tendency in the formation of suppletive demonyms for macrotoponyms are the terrain features and the assessment of ethnic background or mentality. The analysed demonyms manifest the relations of intralingual, intervariant homonymy, as well as hypo-hyperonymic relations. The complex analysis of the material has provided an opportunity to represent the demonym systems of Chile, Colombia, Mexico, Peru as multidimensional and at the same time inherent to the unified functional continuum of entity in Spanish-speaking countries. The research results have led to the conclusion that demonyms act as independent notions and generators of new meanings and allusions. It is recommended to use transliteration when translating suppletive demonyms, while their decoding amplifies the linguacultural competence of Spanish-language students and harmonises the intercultural dialogue with the native speakers of Chilean, Colombian, Mexican and Peruvian national variants of Spanish in the areas of education and business.