The game uses various dictionary references for valid words. The list of the main reference per language is shown below.

English - Wordnik

Swedish - SAOL

French - fr-moderne (https://www.dicollecte.org/)

German - Collins

Italian - Zingarelli

Spanish - Either FISE or Collins

Norwegian - Norska Scrabbleförbundets ordlista

Danish - Dansk språkvårds ordlista