Init __localizationCache if it is undefined

[monapochi]

I'd come across this issue, this.constructor.prototype. __localizationCache is undefined in iOS Safari. (Of cause, it's good in Chrome :-) ) I didn't investigate the root cause of this issue, wrote a check code.

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[monapochi]

I've signed it

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[monapochi]

Sorry, I seemed to make a mistake at rewriting the commit log, so delete this pull-req, thanks.