I guess there are two ways of looking at it.

1. As a set of rules that you must abide by in order to make music, or
2. A set of concepts which have have been developed to describe, in words and symbols, what a combination of different sounds are.

So to answer your question, yes and no. Yes, in that if you analyse enough of a person's music you will find a set of musical "ideas" that are repeated enough to be considered someones "harmonic language" as you put it. No, in that almost all music can be broken down into its individual parts and described with conventional analysis and so creating a new "harmonic language" for a single musician/composer seems a little like a waste of time in that we already have a fairly robust set of analysis tools to do such a thing.

I will give you an example that may or may not help. When I was studying Miles Davis, I spent many hours transcribing his solo's from many different era's where he played different styles and with different people. Throughout his entire career, I was able to find ideas he would repeat again and again and again. Licks he would play over early bebop would reappear over his fusion era. Sure if you weren't transcribing the amount that I was at the time, you may not even realise these licks were the same. But sure enough, through conventional musical analysis, I was able to discern patterns and in a way, form somewhat of a basis for harmonic, melodic and rhythmic ideas that you might be able to call his "harmonic language". Although I didn't think of it this way, I thought of it through the lens of conventional analysis.

So I guess, it comes down to definition and if you are willing to forget the idea that music theory is a set of rules and accept that it is just a set of tools.

I guess there are two ways of looking at music theory.

1. As a set of rules that you must abide by in order to make music, or
2. A set of concepts which have have been developed to describe, in words and symbols, what a combination of different sounds are.

So to answer your question, yes and no. Yes, in that if you analyse enough of a person's music you will find a set of musical "ideas" that are repeated enough to be considered someones "harmonic language" as you put it. No, in that almost all music can be broken down into its individual parts and described with conventional analysis and so creating a new "harmonic language" for a single musician/composer seems a little like a waste of time in that we already have a fairly robust set of analysis tools to do such a thing.

I will give you an example that may or may not help. When I was studying Miles Davis, I spent many hours transcribing his solo's from many different era's where he played different styles and with different people. Throughout his entire career, I was able to find ideas he would repeat again and again and again. Licks he would play over early bebop would reappear over his fusion era. Sure if you weren't transcribing the amount that I was at the time, you may not even realise these licks were the same. But sure enough, through conventional musical analysis, I was able to discern patterns and in a way, form somewhat of a basis for harmonic, melodic and rhythmic ideas that you might be able to call his "harmonic language". Although I didn't think of it this way, I thought of it through the lens of conventional analysis.

So I guess, it comes down to definition and if you are willing to forget the idea that music theory is a set of rules and accept that it is just a set of tools.