In the Japanese audio for Advent Children Reno also says "zotto" a lot and, less frequently, "datto". In the English, this is substituted with something like an informal "ya know" or "man", as Wolf Kanno described.

Volgin's use of "kuwabara, kuwabara" in MGS3 could have been translated, but even then he'd just be naming a plant. Without the cultural context, it'd be pretty meaningless to an English-speaking audience. It would've helped if they'd taken a moment to explain the old myth about Mulberry trees, even if it was just in a radio conversation or something.