Is it possible to change the language used in all text styles at once.

@marikap3737523

app.activeDocument.paragraphStyles.everyItem().appliedLanguage = "something";

https://creativepro.com/how-to-install-scripts-in-indesign/

Search-in-Styles (basically find/change inside paragraph styles and character styles) lets you do this (and, indeed, find/change almost anything else in paragraph and character styles): https://www.id-extras.com/products/search-in-styles/

If you make all styles as children dependend of a single root style, you need to change the root style language. All other styles will inherit the chages made in in the root styles.

There is a script installed to chage all languages at once, but it will overwrite properties even there where you want a different language like ine a character style.