[ticket/12451] Split TOO_FEW_CHARS_LIMIT for plurals

PHPBB3-12451
[ticket/12451] Split TOO_MANY_CHARS vars for plurals

PHPBB3-12451
[ticket/12451] Use new line to concatenate strings

PHPBB3-12451
[ticket/12451] Remove duplicated lang var

PHPBB3-12451
Merge pull request #2363 from Elsensee/ticket/12451

[ticket/12451] Split lang vars in posting.php for plurals

* Elsensee/ticket/12451:
  [ticket/12451] Remove duplicated lang var
  [ticket/12451] Use new line to concatenate strings
  [ticket/12451] Split TOO_MANY_CHARS vars for plurals
  [ticket/12451] Split TOO_FEW_CHARS_LIMIT for plurals