Need advice on language barrier

Hello,

Listen to the scenario and please give 2 minutes of your time to advice..

* Site is in regional language {Where people dont google in the native language..}
* Niche is not that competitive or too much volume.

How to do SEO for such a site..? Keywords you put in the articles are in regional language but users never google in that language...

I hope I am clear on what I am asking.

Why not just write the article in the main language? If people are Googling in that language surely they understand it, I don't see the benefit of writing the article in a dialect that only a percentage of visitors will be able to understand?

Its hard to search in that regional language but they dont want to read the article in English...
The total population is approx 70 million and readers may be 10 mil target audience...