`customTranslateFunction` is not defined in `getPropertyMap` method with `MagicMerge` class.
It causes Custom Translation Function to not be taken into consideration at all while translating strings.
Solution:
adding `customTranslateFunction' => array('setting'),` key to `getPropertyMap` array resolves the issue.
'backtrace' => array('setting'),
'contact_default_language' => array('setting'),
'countryLimit' => array('setting'),
+ 'customTranslateFunction' => array('setting'),
'dateInputFormat' => array('setting'),
'dateformatDatetime' => array('setting'),
'dateformatFull' => array('setting'),