Translation Management Event Log shows entries with CREATETRANSLATION failed: Unable to complete your request, you are not allowed to alter logical object.

Action:   CREATETRANSLATION failed
Description:   CREATETRANSLATION failed with error: Unable to complete your request, you are not allowed to alter logical object "GUID-XYZ". [c:8484 ce:GUID-XYZ ct:CTLIB]
Status:   Failed
Event level:   Exception

What could be the reason for 'you are not allowed to alter logical object'?

Check the security that is set on the folder where the mentioned object is located in. You can use search - locate to find / locate the object in the repository.
You know now who can write to the objects in the folder.
Then check the groups where the ServiceUser user belongs to.
If the ServiceUser user does not belong to the user group that is set as owner of the folder you get this kind of permission errors.
Add the ServiceUser to that group.
It is best practice to assign the ServiceUser to all user groups to avoid this kind of security problems when translating.