Multilingual: allow removing translation using "$NULL" keyword.

(cherry picked from commit adab83b9101ccde17e83da584a1668aa68c5a7a6)
Translations:

-Fixed new translation key file not being created
-Added ability to remove translation on import using keyword "$NULL"

(cherry picked from commit 014beedda3ea26de209b80886e5ced842b0563d9)