CMS login causes ExtJS Javascript error

The CMS logs a Javascript error when a user logs in. Steps to reproduce:

1. open Firefox and enable the Firebug console
2. start GoGreen locally with "mvn -Pcargo.run"
3. log in to the CMS as admin with the English language selected

Expected behavior: no Javascript errrors are logged
Actual behavior: the following Javascript error is logged:

"Ext is not defined"
in ext-lang-en.js at line 15:
Ext.UpdateManager.defaults.indicatorText = '<div class="loading-indicator">Loading...</div>';

The error is caused by the wrong order in which the ExtJS javascript sources are loaded: ext-lang-en.js is loaded before ext-base.js and ext-all.js, so the Ext object does not exist when ext-lang-en.js is evaluated.