A system standard does not exist yet. & cannot be created.

What causes this issue?

You tried to create an application standard or an exception.

System Response

No system standard exists yet for this source text. However, the first
translation of a source text must become the system standard. You can
create an application standard or an exception as soon as a system
standard exists.

How to fix this error?

First enter the target text that you would create as the system
standard. Choose save so that it becomes the system standard. You can
then create the required exception / application standard.

Error message extract from SAP system. Copyright SAP SE.