The main difference is that German SCHOTT glass has slightly better light transmission.
German Schott B270 optical glass is highly resistant to solar radiation and offers high transmittance in the visible wavelength range. It also has high chemical stability and a fire-polished surface providing excellent image sharpness. The Japanese Optical glass is also a very high-quality optical glass with a very similar light transmission – 99.6% versus the German Schott B270’s 99.8% light transmission.
It is very hard to see the difference in image quality unless using telephoto lenses (focal length >100mm) or enlarging images to be printed in large formats.