The translation pack must include the following files:

• html-files, containing help pages;

• the conhelp_en.php file containing context help messages; 
  

• the messages_en. php file containing system messages.

Note:
Messages from the messages_<LocaleID>.php file might include a substitution variable. At that, the number of this substitution variable is important. Please, have a look at the following example:  

let's consider the "Enter %1 for %2:" phrase with the substitution variables_ ("Enter %1 for %2:", "Login", "FTP") = we will receive => "Enter Login for FTP:" 

at the same time, this phrase may look different in another language, such as, for example, "Enter %2 %1 :" _("Enter %2 %1:", "Login", "FTP") == we will receive ==> "Enter FTP Login:"