Use an Event Handler to Reference Messaging for Web Custom Labels
From Setup, enter Deployment, and then select Embedded Service Deployments.
To the right of your deployment’s name, click the downward arrow, and then select View.
In the Custom Labels section, select Edit Custom Labels, and then create your translated labels.
Access the label framework for your deployment by using this.configuration.standardLabels for default text and translations or this.configuration.customLabels for custom labels created in the Custom Labels page.