Provide a thin wrapper around toLocaleString()

While this still doesn't offer a consistent and predictable experience due to
browser inconsistencies when it comes to `toLocaleString()` implementation, it
is the least bad option we can easily offer for the time being.

Refs. #59.

pootle/static/js/browser/components/ColoredNumber.js

@@ -8,6 +8,8 @@
 
 import React from 'react';
 
+import { toLocaleString } from 'utils/i18n';
+
 
 const ColoredNumber = React.createClass({
   propTypes: {
@@ -19,7 +21,7 @@ const ColoredNumber = React.createClass({
       return <span className="zero">0</span>;
     }
 
-    return <span>{this.props.n.toLocaleString()}</span>;
+    return <span>{toLocaleString(this.props.n)}</span>;
   },
 });
 

pootle/static/js/browser/components/NumberPill.js

@@ -8,6 +8,8 @@
 
 import React from 'react';
 
+import { toLocaleString } from 'utils/i18n';
+
 
 const NumberPill = React.createClass({
   propTypes: {
@@ -25,7 +27,7 @@ const NumberPill = React.createClass({
         className="stats-data"
         href={this.props.url}
       >
-        {this.props.n.toLocaleString()}
+        {toLocaleString(this.props.n)}
       </a>
     );
   },

pootle/static/js/shared/utils/i18n.js

@@ -107,3 +107,20 @@ export function nt(singular, plural, count, ctx = null) {
   }
   return interpolate(ngettext(singular, plural, count), ctx, true);
 }
+
+
+/**
+ * Locale-specific to-string conversion.
+ *
+ * This is a thin wrapper around `.toLocaleString()` to always use
+ * `navigator.language`, which is the least bad option we have to determine
+ * user's preferred language for the time being.
+ *
+ * Please note browsers implement `toLocaleString()` very differently and when
+ * it comes to number decimals, it doesn't work at all in Safari 9 and IE11,
+ * Chrome always omits the parameter passed to `toLocaleString()` and Firefox is
+ * the only one obeying it.
+ */
+export function toLocaleString(number) {
+  return number.toLocaleString(navigator.language);
+}

pootle/static/js/stats.js

@@ -19,6 +19,7 @@ import LastActivity from 'components/LastActivity';
 import TimeSince from 'components/TimeSince';
 import cookie from 'utils/cookie';
 import { q } from 'utils/dom';
+import { toLocaleString } from 'utils/i18n';
 
 import BrowserTable from './browser/components/BrowserTable';
 import Stats from './browser/components/Stats';
@@ -27,7 +28,7 @@ import msg from './msg';
 
 
 function formattedValue(n) {
-  return n ? n.toLocaleString() : 0;
+  return n ? toLocaleString(n) : 0;
 }
 
 function nicePercentage(part, total, noTotalDefault) {