I'm not sure about the Japanese cartridges but 4 of the easiest ways are the color, the label, the back, and the contacts.
it's a little hard to tell but the color of the one on the left is a little lighter shade of gray and you might see fonts are off on the label (gameboy advance logo for this one)
![](http://i1324.photobucket.com/albums/u615/WhyDo_iHaveThis/c82fa366-2bfb-4ea1-ac9f-914d68cbbe72_zps1ad57b7c.jpg)
the font on the back of the cartridge will tend to be larger and not as bold
![](http://i1324.photobucket.com/albums/u615/WhyDo_iHaveThis/6d085540-7356-477f-8b53-d7d940e9bc6d_zpsa01a4fd6.jpg)
finally the nintendo logo should appear like this above the contacts
![](http://i1324.photobucket.com/albums/u615/WhyDo_iHaveThis/c893c8ba-a9b4-49ae-88a5-e3933927b935_zpscee075e3.jpg)
Not like this
![](http://i1324.photobucket.com/albums/u615/WhyDo_iHaveThis/4d2eb127-0b95-49c2-9057-cd92a766d06e_zpsa7173a83.jpg)
Hope this helps