Hi Gundriveth,
You're asking a really good question. In general, my advice to friends or clients who are not graceful in a language they want to release their game in is to find someone who
is graceful in that language and get their help in localizing the game's text. Judging by this post, your command of English is pretty proficient - you can communicate your ideas clearly with other speakers - but it is not graceful yet.
Even occasional errors in grammar or word choice can break a player's immersion in your plot or gameplay, because the player feels like she's reading something that someone else wrote, instead of feeling like she's reading something that's happening in front of her. That's why it's so important to get someone who can speak the language with power and grace.
I've volunteered to handle the English localization for a few good-looking games in the past, so I have a lot of experience in perfecting the English for dialogue and other game info - but it's a time-consuming effort, and these days I'm too busy to do it on a volunteer basis (except for the most spectacular-looking projects), so at this moment I'd only be willing to do it on a paid basis. (However, I did take a look through your portfolio, and I have to say that your paintings and illustrations are
beautiful!! Later this year, I would probably be willing to handle your game's localization if you haven't found help by then, in return for creating some art for my game.)
I think that
@Ms Littlefish gave you a great suggestion - you might be able to find someone to help you on the Project Recruitment subforum, since this site has a lot of native English speakers. Explain what you need, but also explain why your project is great and why a volunteer would want to join it.

Posting in the Classifieds (paid work) subforum will give you an even better chance to find someone that is committed enough to complete the job, but I recommend using this as a last resort, since you might be able to find someone to help you for free if your project looks appealing enough to join.