Fix translations for NSDate+SAMAdditions

While using good old SSToolkit (<3), I've noticed that this localized string key looks wrong in several translations:

https://github.com/soffes/sstoolkit/blob/master/Resources/zh_Hant.lproj/SSToolkit.strings#L20

(Even without looking at the translations, it's a duplicate key.)

Nothing in this PR has been tested manually or automatically, and I have only looked at a few languages so far. I have verified my changes to the Chinese translations with a native speaker though. Will push more commits if I get a chance, but feel free to discuss and merge/reject this already.