Functional language is exactly that. Functional language is the communication that is used in order to effectively obtain what you want or need. It is purposeful. Without its use, language has no true meaning so this is a goal that we want to see achieved in anyone who is learning to speak one fluently. If you were to learn a foreign language in an online course, here is an idea of how it might be taught and learned. https://www.netlanguages.com/blog/index.php/2017/08/28/what-is-functional-language/
Scripted Language may not be as familiar a term to you:
Scripting is a parent-directed way of teaching children to use functional language to meet their needs and wants. It may be used in children who are diagnosed with Central Auditory Processing (CAPD). Here is a link to give you examples of how this works and as well, how you could use this as a teaching tool for your child at home who is diagnosed with this deficit. https://www.friendshipcircle.org/blog/2014/05/13/building-speech-language-practice-into-your-childs-day/
Scripted language can manifest itself in the repetition of words, phrases, intonation, or sounds of the speech of others, sometimes taken from movies, but also sometimes taken from other sources such as favorite books or something someone else has said.
People with Autism often display scripting in the process of learning to talk and I mention it because if you are a parent who is reading this or a professional interacting with a person who is “scripting” you want to understand it and not necessarily become neither irritated nor confused by this type of behavior. There are different types of scripting: echolalic and social. Consider the following resource: http://www.thespeechmama.com/2011/10/07/how-to-teach-a-child-with-autism-to-talk/