Add spanish translation

[6ig6oy]

New Issue Checklist (tick off like this: [x])

• [x] I checked existing issues (open and closed) for possible duplicates
• [ ] I can reproduce the problem on the latest stable version (not nightly!)
• [ ] If you have a problem with a specific website: adding the domain to your no-skip-urls-list does not solve the problem
• [x] The issue is not about adding entries to the default no-skip-urls-list

What is your browser?

• [x] Firefox
• [ ] Chrome

What is your operating system?

• [ ] Linux
• [ ] Mac
• [ ] Windows

Description (please include examples/screenshots where applicable)

Hello, I was just wondering if you could add locales/es to your fantastic extension.

It would be interesting to have a website like weblate.org to make translations.

I hope you find the translation useful, greetings

PD: Sorry, I was unable to open a pull request.

locales_ES.zip