Explore implications of not sending an ACCEPT-LANGUAGE header
In Bug1039069 (and previously in legacy/trac#1110 (closed)) Tor Browser (and previously torbutton) provide an option for spoofing the ACCEPT-LANGUAGE header as en-US. In #30605 (closed) we're deciding how we should handle this on Android. However, the question, itself, seems suspect. We want to create the smallest number of Tor Browser user sets as possible, and bucketing "most" users into "prefer English web pages" is one way of accomplishing this (and it benefits the English-speaking world), but that forces non-English speakers into the difficult choice of leaking their preferred locale or possibly receiving a web page in their non-native language.
We should think about the implications of not sending the ACCEPT-LANGUAGE header, entirely, instead of spoofing it as en-US.