Frederic,
Thank you for writing to us.
If your required language is not available for SJB. You can suggest a translation on WP GlotPress platform. Following is the link where you can translate Simple Job Board in your language:
https://translate.wordpress.org/projects/wp-plugins/simple-job-board
Please add translations against each string, once these translations will be approved by GlotPress team then it will be the part of SJB plugin and you can update it through the WordPress Updates page.
Another way to add translation is to copy the simple-job-board/languages/simple-job-board.pot file somewhere else and then translate its strings into Spanish. After completing the translation task, get back to us at support@presstigers.com with this file so that we can provide the compiled file.
Please let us know if you need any further assistance.
Regards,
