David Morales's answer is correct.. or at least that was the exact issue I was running into as well. 

I followed every step multiple times in creating the language translation file, but nothing seemed to work. My module was named with '-', ie. my-custom-module. 

I renamed the module and project to use '_', ie. my_custom_module and restarted odoo instance and voila... my module picked up all the spanish translations just fine! 

I'm following the same steps as you and no problems on versions 12.0 or below, but in 13 I can't get the translations to work thought the error I get is different:

2020-01-30 19:48:23,325 459 ERROR industrial-supplies odoo.tools.translate: malformed po file: unknown occurrence: model_terms:ir.ui.view,arch_db:industrial-supplies.external_layout_background_custom_address

This is directly exported from odoo, just downloaded the po and uploaded and I have the error message.