Multilingual campaigns

[DmitriyKulagin]

Allow a store owner to specify "Subject" and "Body" for different languages (like we allow for products, categpries, etc). And then we can use it based on the language specied for newsletter subscription (see #6978)

[BuddhiEash]

Do you mean to add a dropdown to choose a language when creating a campaign, and show the campaign if the store's selected language matches with the campaign's language?