lang='ja' + system lang en -> 'Japanese' font lang='en' + system lang ja -> 'Japanese' font lang='en' + system lang en -> 'Chinese' font
For example, on Windows 10+ with system font stack without system-ui:, lang attribute and the system language are probably used to determine the fallback order.
I'm pretty sure the font choosing algorithm takes into account the 'lang' attribute as well.
