Is it a good idea?
Probably not, but as always: it depends.
Your theme may be using this setting in the html element to flag the used language of your content to the browser. lang - HTML: HyperText Markup Language | MDN This may break if you try non standard stuff here.
Although Apple is a big company, those companies may not be right with their choices 100% of the times.
I would stay with the standard way!