3251311 - It's not possible for the user to Import/Export files in the category as the button is missing.

User was granted V, W, P, D rights in one of the Dictionary categories. However, it's not possible for him to Import/Export files in the category, the button is missing.

Most likely the reason is because the feature set of General - Dictionary Import/Export has not been enabled for the user's group.

Please enable the feature set and see if the Import/Export button appear?
1.Open the Explorer and click Setup - Manage users & access rights
2.Go to the User groups tab 
3.Figure out the user group where the user belongs to and select it and activate the feature set.

For more details please refer to : Activate feature sets

KBA , BPI-SIG-PM-DIC , Dictionary for SAP Signavio Process Manager , How To