I have created a new translation for Spanish (es_ES) since it was incomplete.

[adaniieel]

I tried to follow the guidelines from the repository to join https://poeditor.com/join/project/37SpmJtyOm, but it is not currently allowing me to join.

Steps I followed to obtain the new translations:

1. Installed gettext on my local server.
2. Ran a script on all PHP files again to generate the .pot.
3. Created the .po file.
4. Carefully translated everything with ChatGPT.
5. Created the .mo file.
6. Replaced it in /locale/es_ES/LC_MESSAGES/.
7. Tested the changes, and they were reflected.

There are a couple of bugs to fix in the PHP files for some texts, but if you accept this, I will create a separate one for that.

I hope this contribution is helpful.