Need en-US locale in MDN URLs
Need en-US locale in MDN URLs

When locale doesn't contains the MDN URL, MDN redirects to the localized page
which contains a UA's locale, but there are cases have gone to not found page.
It avoids this problem by specify `en-US` locale clearly.

alexduch/jpm,rpl/jpm,wagnerand/jpm,guyzmuch/jpm,jsantell/jpm,jsantell/jpm,alexduch/jpm,johannhof/jpm,benbasson/jpm,Medeah/jpm,nikolas/jpm,mozilla-jetpack/jpm,freaktechnik/jpm,Medeah/jpm,freaktechnik/jpm,nikolas/jpm,mozilla-jetpack/jpm,johannhof/jpm,guyzmuch/jpm,mozilla/jpm,mozilla-jetpack/jpm,wagnerand/jpm,matraska23/jpm,mozilla/jpm,benbasson/jpm,Medeah/jpm,mozilla/jpm,kkapsner/jpm,matraska23/jpm,jsantell/jpm,johannhof/jpm,rpl/jpm,wagnerand/jpm,alexduch/jpm,nikolas/jpm,kkapsner/jpm,freaktechnik/jpm,benbasson/jpm,kkapsner/jpm,rpl/jpm,guyzmuch/jpm,matraska23/jpm