Use empty array instead of empty string

Documentation says to pass `undefined` or an array. 
An empty string is not supported upon closer inspection.
Recommended not to pass `undefined` as it might cause weird quirks.
People recommend using empty array.

website/client/src/filters/localizeNumber.js

@@ -12,7 +12,7 @@ export default function localizeNumber (valIn, lang, optIn) {
 
   return val.toLocaleString(
     // Catch null just incase
-    (lang || '')
+    (lang || [])
       // Strip beyond @ symbol to allow custom languages
       .replace(/@(?:.+)$/, '')
       // We use underscore, this mthd uses dash