Value & entered more than once

What causes this issue?

You have already entered values for this characteristic. You are
entering new values, and have entered the value &v1&. This value exists
already.
The system also compares the neutral values to their language-dependent
value descriptions. If a combination of neutral value and value
description is not unique, you see an error message.
Example:
Neutral value,,Language-dependent description
yes,,no
no,,yes
In these combinations of value and value description, the system cannot
interpret the values "yes" and "no" uniquely. It therefore rejects the
combinations.
Note
The system checks the combination for all languages in which you
entered value descriptione.

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?

Enter a value that does not yet exist.
Make sure that the neutral values and the language-dependent
value descriptions are unique in all languages.

Error message extract from SAP system. Copyright SAP SE.