Hello,
Ad. 1 – in Email tab under Email message to User/Admin you can find Show email variables – using them you can write and translate your message anyway you want – for example instead of {fields} for all fields you can type something like this:
Name: {name.value}
E-mail: {email.value}
You can find field aliases (name, email etc like in the example) in Fields > Advanced options for a field.
Ad. 2 – yes, however for now our plugin is only in English, if you are using pages in multiple languages, you can copy our forms, translate the labels as you wish and use them by displaying them through shortcodes for different languages.
Ad. 3 – yes, you can use HTML code as the success message
Best regards