There would come problem on language strings when you we place moodlemobile2 folder under www folder of System for any mobile app customization.

Like if I have centos operating system, which has folder structure something like,
var/www/html, If I do something like var/www/html/mycustomapp, then the error would come something like,

*'mma.files.myprivatefiles' | translate

'mma.files.myprivatefilesdesc' | translate

'mma.files.sitefiles' | translate

'mma.files.sitesdesc' | translate

'mma.files.admindisableddownload' | translate

'mma.files.clicktoupload' | translate

'mma.files.clickupload' | translate

'mma.files.uploadfile' | translate*

It happens because, the language file is existing in www folder mycustomapp/www/core/language

By this line var path = file.path.substr(file.path.indexOf('/www/') + 5, file.path.length-5);
at treatFile() in gulp.js near about line numbder 66 tries to get the language file from var/www/core/language but our real structure is something like var/www/html/mycustomapp/www/core/language. According to above line, it gets the first www which has not language files, so language strings can not be converted in real language.

Discussion can be found at Here