I don't believe you can customize that message.
Here is just a though: Place the "EmailService" component from "Foundation" category in your process where you want to send the notification email, then go to its "Properties > Contents" to customize the email message.
Jasmin, can you confirm if it work this way.
Yes and No.
Using the email service from Foundation will work. You'll get an email with the customized message but you'll still receive the built-in message from the TaskManager service when you complete the task.
The message you want to customize is the SMTP message coming from the email provider as a result of a send to the email endpoint.
This is not exposed in 8.2.1. (However, it is exposed on the email endpoint in 9.0.)
NOTE: This doesn't apply just to the Complete Task but to any email endpoint you add to any service.
The same message is sent by the email provider for all success/failure messages.
By default, even for 8.2.1, we do provide this message in English, French, German and Japanese.
The language that your end-users will receive for their success or failure message depends on the OS language that your LC server was bootstrapped in.
For example if your LC server is installed on a French OS, those messages will be in French.
If you need something other than English, French, German or Japanese you can still customize this with a workaround.
The strings you want are located inside the adobe-emailprovider-dsc.jar.
If you open this file, you will find the ApplicationResources_en.properties file.
You can set the message strings to your requirements.
Thank you, this is just what I needed