problem with spanish translation appointments+

I have a problem with the spanish translation of this plugin. I try to use the translation but is incomplete and when I try to complete the front end translation I see that the fields that I need are translated in the .po file but in the front end it still remain in english. In the attached file you can see that the form is half in english and half in spanish. I think that in the font code it isn't translatable strings. How can I solve this or which file can I edit to change the sentences?

Thanks a lot