Though languages are often associated with one primary writing system, often another can be adapted for use.
Look at how Vietnamese was classically written with a form of Chinese characters, but in modern times is written in Latin script using a system adapted from Portuguese.
I think your question is still a good one (which I don't know the answer to) but it's worth being precise with the terminology :)
https://en.wikipedia.org/wiki/Hinglish says
> In India, Romanized Hindi is the dominant form of expression online. In an analysis of YouTube comments, Palakodety et al., identified that 52% of comments were in Romanized Hindi, 46% in English, and 1% in Devanagari Hindi.
The most common explanation for use of Romanization online between native speakers of a language that's traditionally written in some other script is limitations of computer systems. Those can include things like
* inconsistent character encoding support (different people or different software systems don't agree on which encoding to use, or some software system actually corrupts or filters out some encodings)
* poor input method support (it's hard to type in some other script on some devices)
* poor rendering support (some software system doesn't display some script well, e.g. failing to render ligatures between connected characters properly)
* legacy of historical software problems (people may have learned to use earlier systems that didn't have good language support, and may have developed workarounds that then persisted because of cultural inertia or individual habits)
* limited literacy (people might not have enough training and practice in a script to be fully comfortable reading and/or writing it, even if they're fluent speakers orally)
Almost every computer system supports ASCII perfectly, and so that can easily become a lowest common denominator for representing various languages. This is not uncommon online with Arabic and Chinese, in addition to Hindustani.
But I don't actually know the answer here; those are just some common trends related to representation of languages on computers...
Python language unicode discussion : https://realpython.com/python-encodings-guide/
https://en.wikipedia.org/wiki/Beta_Code - but people (including Greek speakers) still transliterate Greek to English-style, like https://en.wikipedia.org/wiki/Greeklish
https://en.wikipedia.org/wiki/Romanization_of_Hebrew#Compara... - see "Common Israeli" (despite the existence of scholarly options like SBL, and the fact that the informal transliterations conflate tons of different things that are spelled differently but pronounced alike in modern Israeli Hebrew)
https://en.wikipedia.org/wiki/Romanization_of_Arabic#Compari... - as with Hebrew, the https://en.wikipedia.org/wiki/Arabic_chat_alphabet versions will also sometimes elide differences that are preserved in writing in Arabic script
https://en.wikipedia.org/wiki/Pinyin - but people (including some Chinese speakers) sometimes still transliterate Chinese to English-style (and often omit the tones)
My impression is that, of these, native speakers of the mentioned languages are most familiar with Pinyin, probably because it's officially taught and tested in school in many Chinese-speaking countries. I don't think romanization methods for the other languages are taught in school and that might help account for why many people often don't know them, or at least don't know them in detail.
The writing system that developed with Sanskrit and that's still used for both Sanskrit and several modern languages of India is called Devanagari.
They could also, for example, have support for Nepali, which is also normally written in the same alphabet but is definitely a different language from Hindi. In that case the language support would be different at a software level, like the vocabulary and/or grammatical patterns that the speech-to-text system is trying to recognize.
The problem (whether for a computer or a human being!) of figuring out what language something is actually written in can be tricky when many languages use identical or related scripts:
https://en.wikipedia.org/wiki/Wikipedia:Language_recognition...