i18n: Add new language from Transifex: be (Belarusian)

A quick skim of the new messages_be.json file shows that it isn't
substantially translated, so we don't offer it in the UI yet.

Author: chrisbobbe

flow-typed/translations.js

@@ -12,6 +12,10 @@ declare module '../../static/translations/messages_ar.json' {
   declare export default {| [string]: string |};
 }
 
+declare module '../../static/translations/messages_be.json' {
+  declare export default {| [string]: string |};
+}
+
 declare module '../../static/translations/messages_bg.json' {
   declare export default {| [string]: string |};
 }

src/i18n/messages.js

@@ -14,6 +14,7 @@
 // client, which are based on the language names that appear in Transifex.
 export default {
   ar: require('../../static/translations/messages_ar.json'),
+  be: require('../../static/translations/messages_be.json'),
   bg: require('../../static/translations/messages_bg.json'),
   bn: require('../../static/translations/messages_bn.json'),
   ca: require('../../static/translations/messages_ca.json'),