Sainbury’s, the UK supermarket retailer has a good set of writing guidelines for UX writing as part of their Luna Design System.

See https://web.archive.org/save/https://luna.sainsburys.co.uk/copy/writing-principles

They have also published their writing style guide which can be helpful as a starting point for English-language style guides.

See user experience (UX), writing guidelines, writing, Writing Gallery Text at the V&A