Thanks Sofa_King for sharing the experience, definitely its helpful when followed correctly. Although the issue comes at investing in marketing, could you provide any example of such customer interactive spaces online. This is because i have tried doing this with Facebook pages dedicated to gaming, but the participants are mostly game developers there. For a casual game like the one in this post, i don't know any such interactive space to showcase and build an audience.
It depends on the audience. If your target audience is merely 'casual gamers' it will be far too hard for many reasons.
For the OP, he could perhaps narrow down his audience to 'Young mobile gamers in Vietnam learning English'. With a more target niche like this, he/she can then do research (go to these people and talk to them) and find the appropriate interactive spaces. Without a more targeted niche like that, he is left without much guidance and thus must use the oversaturated and highly competitive spaces like the PlayStore. Not only that, but he could also tailor his app to meet their specific needs, making his app even more appealing.