Well, “early” in the sense of the first few hundred years… A few articles for your perusal, for anyone interested.
When considering Ven. Analayo’s review of the English Dirgha Agama translation (spoiler: not recommended), one of the things mentioned was that the translator into English was referring to the original Indic text as Sanskrit rather than Gandhari.
It seemed to me that the translator was probably just translating the term fanwen 梵文 which was historically used in a fairly broad sense, but in modern times has been equated with Sanskrit. That point made me wonder more about the introduction of the term fan 梵 (=brahma) in its linguistic sense. So I did a little digging to try to understand more about the terminology and when it was introduced.
The first article here attempts to look at the introduction of fan as it applies to language:
The author’s theory is that early on, India was conflated with Central Asia, and so Indic literature was considered hu 胡 literature. One of the ideas in this theory is that hu is sort of a racist and derogatory term for Central Asian nomads such as the Xiongnu, with whom the Chinese had many historical conflicts.
According to the narrative here, as Chinese Buddhists became more aware that Central Asia and India were different, they began to adopt fan, which means something like “brahma”, as a term for all things Indic. Essentially, the idea here is that people were making a mistake for hundreds of years, and then started to correct that mistake.
However, a few years later there was a rebuttal by Daniel Boucher:
It seems the terms hu and fan were used in a more technical sense. Hu was indeed referring to Central Asia, but also shorthand for the Kharosthi script. Meanwhile, fan was used for the Brahmi script. This is shown by demonstrating that hu was associated with qulou (=Kharosthi), and also that translations from texts labelled hu have some evidence of being translated from Gandhari in the Kharosthi script, such as very minor errors that can be traced back to Kharosthi forms, etc.
Much of the interest is really in the details, though. It is interesting to read of a Tang dynasty court minister attempting to argue that because the Buddha was from the Western Regions, he must have been an “evil demon” full of “weird spirits”. And to also realize that Buddhists in China were aware of different Indic scripts, and they cared enough to use specific terminology about them.
We can see that Chinese Buddhists like Sengyou struggled to understand that Kharosthi and Brahmi were used to spell words phonetically. Quite different from Chinese characters. But he seemed to consider Kharosthi, Brahmi, and Chinese characters to all be able to equally convey meaning. And on this last point, they also did not consider Kharosthi and Brahmi to be merely scripts. They were commonly thought to be languages. That makes perfect sense because the Chinese language was often defined in terms of its script (while pronunciation was always changing).
Some folk history is given for Kharosthi and Brahmi, evidently modeled on the story of Cangjie (ca. 2500 BCE), the legendary inventor of Chinese characters. In this story, Kharosthi and Brahmi are the names of two people, and both of their scripts predate Chinese characters… Well, historically we know that wasn’t the case. Chinese characters go back to around 1200 BCE, so earlier than Kharosthi and Brahmi.
Sengyou does seem to be aware of Indic scripts besides Kharosthi and Brahmi, and he cites 64 other Indic scripts, along with some examples. That may seem far-fetched, but the basis for this is a very long list of Indic scripts given in the Lalitavistara. So it is not without some basis. He relates these numerous variations to a much smaller number of changes in Chinese scripts, some of which happened over 1000 years before his time. However, of the various Indic scripts, Sengyou states that Kharosthi and Brahmi are the “superior scripts for our times.”