Hi,
Do you see the other overrides in your website ?
The problem is that I can't reproduce your problem, the translations for this key works goods under my local Joomla 2.5 website.
The text is right translated in the code so the only possibility I see is that, the override file is not loaded correctly (a reason will be an error in the file).
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.