I can imagine that would be difficult! I only speak/write a single language unfortunately. (Apologies to my language teachers in high school and middle school ;-; )
My first thought would be to team up with someone who can translate your writing. This would allow you to write the text and dialogue in your native language, and then let someone take care of making it smooth in another language.
If that's not an option, then I'd suggest using something like Google Docs or Microsoft Word. I actually do this all the time. English is my native language, but I'm no master writer. While using Google Docs or Word won't make things perfect, they'll at least perform a basic spelling and grammar check. I do all my writing in one of those programs, and then copy/paste it into the game engine.
I hope that's helpful to you! Keep up the good work. :)