[ticket/12663] Extract CLI language string into their own file

PHPBB3-12663
[ticket/12663] Have cli.php language file at top level; unrelated to ACP.

PHPBB3-12663
Merge pull request #2751 from bantu/ticket/12663

[ticket/12663] Extract CLI language string into their own file

* bantu/ticket/12663:
  [ticket/12663] Have cli.php language file at top level; unrelated to ACP.
  [ticket/12663] Extract CLI language string into their own file