The Redmi 6 and 6A have been released with MIUI firmware, which is Xiaomi's custom skin on top of Android. While the default ROM is in Chinese, international users can easily flash an English ROM or a Global ROM, which includes English language support.
AOSP / LineageOS / Android Open Source Project-based ROMs Xiaomi Redmi 6 6A Cactus Eng Rom
If you are flashing (to gain root without changing the OS): The Redmi 6 and 6A have been released
is a budget device with specific hardware that dictates which ROMs it can run: : MediaTek Helio A22 quad-core. Storage/RAM : Available in 16GB or 32GB storage with 2GB or 3GB of RAM. Codename : "Cactus" is the specific identifier for the Xiaomi Redmi 6 6A Cactus Eng Rom