Yes, every single setting can be changed via HTTP request.
This HTTP request sets the language of the Phone UI to German.
- Any ASCII character can be generated by using its hex value preceded by "%". Please look at this page for the complete encoding table.
- URLs cannot contain spaces. Encode a space with %20
- If you have set up user name and password to protect the web interface the HTTP request must be authenticated, with your browser you can use the following syntax: http://username:password@phoneIP/settings.htm?settings=save&setting=validvalue
- Hidden tags need to be disabled in order to have the setting change taking effect
If you want to permanently store the value without clicking the "Save" button you need to add the store_settings=save parameter