Translating “Out of stock”

Hi,
I wanted to translate “Out of stock” in .po file, but “Out of stock” is not set in your language file.
I changed the value in line 58 of “sticky-bar.php” file, but to be easier and ok in next updates of plugin, can you add the field “out of stock” in your language file so we can translate it ?
Thank you !
Aude.