Hello.
Indian brokers’ apps, trading platforms, knowledge base etc. are only made in English, and regional languages find no place in such apps.
There are a lot of people, who are not fluent in English, but are more comfortable in their own language.
NSE website is available in Hindi, Marathi, Gujarati languages.
Why brokers do not use Indian languages, so as to expand the investor base beyond the English speaking population in India?
Some markets content is explained and is available in regional languages, and English is not completely alien to the majority of people as English words have penetrated regional languages long ago, and this also helps people to learn.
And I guess it is hard to translate every aspect of markets into regional languages, there may not be precise words in the languages, and even if they are, their usage may not be permitted by the laws that govern the market.
On the tech side, may be it is not possible to code all the features in regional languages.
When it finally comes down to brass racks, in how many languages does one that want “buy” and “sell”?
Your question may have merit, but I’m just bringing it down to the functions the broker is supposed to provide. Cheeky 
what about the stock name/scrip, indicators, Jargons in regional languages ? will it be easy to work?
I don’t think they will be available, unlike sciences like physics and chemistry which are translated into regional languages and are studied in schools and colleges, in the previous decades. Moreover, as the majority of the people who are interested in markets are younger, so as these grow up in a relatively more English speaking world, they are learning such jargon straight away. Also, learning these words for anyone is not difficult if they hear them regularly, they can even do some repetition exercises.
And obviously, understanding how something works, and how it can be used is important, not the language.
Agar samajh gaye to munafa paane mein bhasha had nahi hai 