Na that time more than people, industry was that much willing to support other language films.. It was not at all about first day or weekend in the 90's remember?
The movies used to the reach wide audience. They were willing to give in for a good film that came their way. Plus only those films that were dubbed carefully or to say properly not like now a days where the dubbing itself is so bad with real lame hindi translated dialogues. Whether it's Roja, Anjali, Hindustani, Humse Hai Muqabla, Jeans, Duniya Dilwalo Ki, Dil Hi Dil Mein... infact any Shankar or Mani Ratnam film, you can easily notice the efforts gone into dubbing.
Simple thing to notice in Roja, she's a Tamilian whose husband has been kidnapped & in Kashmir she can't speak to others as she doesn't know a single Hindi word. But in dubbing, that entire part is so beautifully handled that Hindi audience don't even know that Madhoo's main trouble in talking to the army officials was that she didn't know to speak Hindi.