Can't beat that one - but this has happened to someone I know.
He's got his new iPhone - and he is a Yank - living in the UK
So set it up for British English
Asked Siri something and was told that siri could not understand and would he please change his version of English
he did
asked the same question again and was informed that his version of English was not the correct one for his country - would he please change his version of English to the one for his country
He , in disgust changed it to Australian English - siri NOT pleased
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If a thing ain't broke --- DON'T FIX IT
Experienced in making a mess of things

2 x MacBook Pro on OSX 10.6.8 ,Belkin N Wireless Router , [ sssh - and a PC wired lappy using XP Pro ] all on
Virginmedia 20meg