Redmi 6 does not support java. Redmi Note 5 support java through third party support.
What's the difference?
I read on Quora that by not supporting Java I can't go to Play Store.
Java is used for developing Android apps, however Android devices itself never supports executing Java (code) out of the box.
All devices which are certified by Google have access to the Google Play Store. The complete list of certified devices is available at Google:
https://support.google.com/googleplay/answer/1727131?hl=en
In this list you can find for example:
Xiaomi Redmi 6 cereus Redmi 6
Xiaomi Redmi Note 5 whyred Redmi Note 5
Xiaomi Redmi Note 5 Pro whyred Redmi Note 5
Xiaomi Redmi Note 5 Pro whyred Redmi Note 5 Pro
Xiaomi Redmi Note 5A ugg Redmi Note 5A
Xiaomi Redmi Note 5A ugg Redmi Y1
Xiaomi Redmi Note 5A ugglite Redmi Note 5A