how to change language for DataTable

You have to either create a language file and then set it using :

"oLanguage": {
  "sUrl": "media/language/your_file.txt"
}

Im not sure what server language you are using but something like this would work in PHP :

"oLanguage": {
  "sUrl": "media/language/custom_lang_<?php echo $language ?>.txt"
}

Where language matches the file name for a specific language.

or change individual settings :

"oLanguage": {
  "sLengthMenu": "Display _MENU_ records per page",
  "sZeroRecords": "Nothing found - sorry",
  "sInfo": "Showing _START_ to _END_ of _TOTAL_ records",
  "sInfoEmpty": "Showing 0 to 0 of 0 records",
  "sInfoFiltered": "(filtered from _MAX_ total records)"
}

For more details read this : http://datatables.net/plug-ins/i18n