1. Navigate to where Hexa is installed (../Steam/steamapps/common/Hexa)
   
2. Open the StreamingAssets/Workshop_Staging folder
   
3. Add an image for you workshop item (Should be 636px by 358px and in either .jpg format). Call this image workshopPreviewImage.jpg
   
4. Create a folder called Localization
   
5. Inside this folder create another folder with the name of the language you are translating
   
6. Navigate to ../StreamingAssets/Localization/English and copy the data.json file into the folder you created in the step above.
   
7. Edit the data.json file with the translation for your language.
   
8. In Hexa click on Tools > Upload To Steam Workshop and select item type as Other. Fill in the rest of the details and upload.

To summarize the only 2 files you need are:

StreamingAssets/Workshop_Staging/workshopPreviewImage.jpg
StreamingAssets/Workshop_Staging/Localization/YOURLANAGUAGE/data.json