A string in update-notifier is not translated

In 14.04, sometimes a red exclamation mark with a triangle appears in the notification area, saying "The update information is outdated. This may be caused by network problems or by a repository that is no longer available. Please update manually by selecting 'Show updates' from the indicator menu, and watching for any failing repositories." And it's not translated.

There is a similar string:

https://translations.launchpad.net/ubuntu/trusty/+source/update-notifier/+pots/update-notifier/zh_TW/+translate?batch=10&show=all&search=check+for+updates

But this one is different.