I permitted anonymous users to translate using l10n client (my local site) so I can translate strings logged in users can't see, like captcha.
When translating as anonymous I can see the translation turns green, but when I reload the page it's not there (I also checked the .po file).
The permission I gave to anonymous users are
l10n_client modul use on-page translation
locale modul user interface
I had to use gtranslator on the po file and imported it to get those strings translated.