The aim of this paper is to determine whether all languages in the linguistic repertoire of a multilingual speaker manifest cross-linguistic influence (CLI) and establish the directions of CLI on the basis of chosen vowels from the linguistic repertoire of two groups: the Bilingual group (L1 Polish/L2 Danish) and the Multilingual group (L1 Polish/L2 Danish/L3 English). The results show that L1 Polish vowels are higher and fronter as a result of the influence of L2 Danish and L3 English. L2 Danish vowels are backer as a result of L1 Polish. Also, L3 English vowels are produced on target, possibly due to combined CLI from L1 and L2. The only direction of CLI that is not observed is from L3 to L2. The existence of a global language system is postulated, which should be treated as one entity whose characteristics depend on the characteristics of its component languages. Each component language has unique features because it is influenced by other component languages in a particular global language system. It is shown that the L1 of a bilingual group is different from the same L1 of a multilingual group because the latter also has a third component language.