Articulate Storyline 360 adds a language attribute to the HTML tag in your published output to identify the course language for screen readers.
You can see the language identifier by opening the story.html and story_html5.html files in a text editor, such as Notepad. The language identifier is on the second line of code. For example, it'll be
lang="fr-FR" for French (France).
You don't have to do anything to enable the language identifier. It's always enabled. It matches the language you select for your player text labels.