Very easy, first check you have downloaded the correct 'System Prompts' - within management console Settings - System Prompts.
If you click on 'Manage System Prompts' you can see which ones are downloaded by clicking in the 'Active Prompt Set', if you language is not downloaded come out of this window - click on Update and select the correct language.
Edit your Digit Receptionist and change the 'Digital Receptionist Language'