To change the language in the epic store, you can create a lauguage.cfg file in the local folder. By default it will be installed in the folder below. The location will vary if you have change your installation folder
C:\Program Files\Epic Games\CostumeQuest\Data\Config
To create a CFG file, create a new text file and open it. Paste one of the language strings below. Do not copy the bolded language, that is only there to highlight which language the string represents.
FRENCH language = 'frFR'
ITALIAN language = 'itIT'
GERMAN language = 'deDE'
SPANISH language = 'esES'
After you have pasted the string onto the text file, select "Save As", to save the file and name it exactly as the text below.
Afterwards launch the game and it should load into the selected language.