Language-dependent Mime object &1 not written (long text)

What causes this issue?

Defined system language &V2& and language of the data to be written
&V3& do not match.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.