After upgrading to MS Dynamics CRM 2013 (build 6.0.000.0809) from Polaris (build 5.00.9690.3233), you will notice that the base language translations remain intact for business process flow labels but the MUI translations are not carried over. You can follow the steps below to restore the missing translations:

1. Set your base language as the user language (Options -> Languages -> User Interface Language)

2. Go to Settings -> Customizations -> Customize the System and click or tap Export Translations to export the labels and their corresponding translations. Save the exported translations zip file locally.

3. Open the translations zip file. Copy and edit the CrmTranslations.xml file in MS Excel.

4. In the Localized Labels sheet, you will notice that the values for Workflow Categories rows (represents the business process flow labels) are blank for the non-base languages.  

 

5. To fix this, look for the ComplexControl values under the Entity column (in the same sheet) and search for your business process flow labels. Copy the non-base language translations and paste them on the corresponding workflow category rows (see step 4). Save.  

6. Copy the updated CrmTranslations.xml file into the exported translations zip file.

7. Reimport the translations zip file by going into Settings -> Customizations -> Customize the System and click or tap Import Translations. Select the updated translations zip file and import. Publish all customizations as needed.

8. To validate that the labels are indeed translated correctly for the non-base languages, switch your user language to a language for which the translations were updated (e.g. German or 1031 for the above screenshot), and open an entity form which contains the business process flow that contains these updated translations. You will now see the correct translations for the stage and step labels.