Set iD.detect().locale to requested locale (closes #2672)

When locale is passed in, we should use that locale in
the parts of the code that are using iD.detect().locale:

* tag reference
* localized name display
* map scale
* info box

The one exception is when iD detects 'en-US' and openstreetmap
website tries to pass 'en', leave it as 'en-US'

js/id/id.js

@@ -58,9 +58,15 @@ window.iD = function () {
         return context;
     };
 
-    context.locale = function(_, path) {
-        locale = _;
+    context.locale = function(loc, path) {
+        locale = loc;
         localePath = path;
+
+        // Also set iD.detect().locale (unless we detected 'en-us' and openstreetmap wants 'en')..
+        if (!(loc.toLowerCase() === 'en' && iD.detect().locale.toLowerCase() === 'en-us')) {
+            iD.detect().locale = loc;
+        }
+
         return context;
     };
 

js/id/ui/scale.js

@@ -1,11 +1,11 @@
 iD.ui.Scale = function(context) {
     var projection = context.projection,
-        imperial = (iD.detect().locale.toLowerCase() === 'en-us'),
         maxLength = 180,
         tickHeight = 8;
 
     function scaleDefs(loc1, loc2) {
         var lat = (loc2[1] + loc1[1]) / 2,
+            imperial = (iD.detect().locale.toLowerCase() === 'en-us'),
             conversion = (imperial ? 3.28084 : 1),
             dist = iD.geo.lonToMeters(loc2[0] - loc1[0], lat) * conversion,
             scale = { dist: 0, px: 0, text: '' },