Thank you for your post.
Under System Preferences, click on "International". Click on the Language tab to set the default language. Click the Formats tab to set your date format as well as Time and Currency formats. This allows you to have Japanese language while using United States date format. Is this what you are looking for? If not, please let me know.
I have a problem my files are showing dates as d/yyyy/m
I need them to be m/dd/yyyy
Yes I can formate to display by why is my default the d/yyyy/m?
"Yes I can formate to display by why is my default the d/yyyy/m?"
Because your file was created under that d/yyyy/m format. Create an empty clone of your file (be sure your International settings are as you want them) and then import data from the original file into the clone. It will inherit the correct settings.