new es-AR fr it nl zh-TW locales

thx BabelZillians profediego, Goofy, Jojaba, nico, Underpass, markh,
Velociraptor !
add preferences item to popup menu
add locales for preferences item in popup menu
* fix detection of account deletion/addition (see b3869630)
* cleaning (use fixIterator on MailServices.accounts)

thx mailInstrumentation !