Currently it simply states Choose files or drag here, is there a way to modify this text so I can add another language?

Also, when I make selection to allow uploading folders, then on clicking the option to upload individual files is gone.

Hello Don,
 
Thank you for reaching out to us.
 
You can certainly translate that message for any language from the forms Set up -> More -> Language section. Here is a quick tutorial for reference. 
 
In regards to the second matter, this is currently the normal functionality of the File Upload field. It can only allow for folder uploads or file uploads, but not both at the same time.
 
Thank you for understanding and please let me know if you need assistance with anything else.