We’d expect that to work and I believe it did work in the past with the lc_time_names changed - I’ve created an issue about it, we will investigate it further and perhaps make those changes a bit easier and user friendly (ie without the need to make direct database changes).
After setting the lc_time_names on the command line, getting a week day with a command line instruction results in a day in the correct language. Is there a change that xibo is resetting the language?