The boy asked in a flat voice, " Lady … are you rich?""

“太太，您富有吗？”男孩子语气平缓地问道。

youdao

The flat voice acting aside, sound design is also fine, with some nice touches like the occasional burst of birdsong.

FORBES: Review - Carrier Command: Gaea Mission

In the audiotaped interview, Hendricks doesn't cry much and her voice sounds flat, emotionless and tired much of the time.

NPR: APNewsBreak: Prayers Before SC Woman Killed Family

His voice was confident and rather flat, with a gravelly distinction.

NEWYORKER: Mr. Bones