This is the notification WhatsApp will send when you use voice message transcription for the first time (Source: WABetaInfo)
WhatsApp is giving users on iOS an option to get transcripts of voice messages they receive. According to WABetaInfo, the company is working on a new voice message transcription feature done entirely on your device, meaning Facebook and WhatsApp won't get access to these messages. It's an optional feature that can also help Apple improve its speech recognition tech.
Those who opt-in to use the feature will see a new Transcript section where you can jump to a specific timestamp. WABetaInfo reports that when a message is transcripted for the first time, the transcript will be saved locally in the WhatsApp database, so there won't be a need to transcript it again for later. The feature is still under development, so public beta testers can't access it for now.
Source: 9to5Mac