The iPhone's personal assistant now understands and speaks Russian, Danish, Dutch, Swedish, Portuguese (Brazil), Turkish and Thai in addition to English, French, German, Japanese, Mandarin, Cantonese, Italian, Korean, and Spanish.
It may be some time before this functionality is available to the public. Apple has yet to release iOS 8.2 to the public despite iOS 8.3 already being available to developers.
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Complete list of newly supported languages: Danish, Dutch, English (India), English (New Zealand), Portuguese (Brazil), Russian, Swedish, Thai, and Turkish.