I have noticed that japanese make a lot of spelling mistakes, generally on the same sounds. I found it strange at first. But then I realized the reason I dont is because I know how to spell them in French. Take grammar, for example, japanese almost always write it as grammer because this writing is closer to the pronunciation. And if I don't make the mistake, it is because the word in French is 'grammaire', so I remember to write it with an A. What are the sounds you find difficult to spell ?