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Что это Русском язык "equivalent" для англиски слово "Wow!"?
Most often is "Ого!" but it can depend on context.
There's also "Ух ты!" as an exclamation of excitement, surprise or admiration, but it's more rare now, after "Wow" made an apearance in our speech.

Soviet cartoon titled "Ух ты, говорящая рыба!" (Wow, Speaking Fish!)