Now that "System Preferences - Language and Region" on Mac OS lets user specify their 'Language preferences" and we stopped supporting Mac OS 10.8 or earlier,  we can remove 'Settings - Languages' on Mac OS. 

Before Mac OS 10.9 (to be verified), it's not the case and we had to add that UI to Mac Chrome. 

Instead of having our own UI, HTTP accept-language values should come from the OS list. 
(see  bug 616965  for a related issue on Android) 

A couple of downsides: 

1. the list of language variants for users to choose from on Mac OS X (Language and Region) does not include some regional variants that are available in Chrome's Settings - Language. 

2. Currently, Translate-related preferences are also controlled in Settings - Language. We need to figure out how to deal with this.