Hi MIguel,
Thank you for your inquire.

We do have Spanish translation for our plugin so you can use it in Spanish language.

And if I have a multi-language site could I use Spanish and English?

You can use it in multilanguage but unfortunately not everything can be translated.

Service names, categories names and notifications can not be translated in both languages.

For this case we suggest to use the plugin on 2 different sites, one for English and one in Spanish.

Best regards.