Nevermind, I found a solution here but I´m not able to post links
If anybody is interesting here is the guide
I am not responsible if you break or otherwise bootloop your phone. If you attempt this you should have the knowledge of how to fix any issues you encounter by trying this guide.
With that out of the way, here's what you need:
- An unlocked bootloader
- The China Developer ROM for your device
- The ROM you want the Chinese theme manager on
- ES File Explorer or any Root Explorer
- build.prop editor
Start by flashing the China Developer ROM to your device. Once you flash this you will need to open up your root explorer and copy the "cust" folder somewhere else.
You may now flash to your desired ROM, which for me was the Xiaomi.eu ROM. Ensure your new rom has root, or root it yourself.
Install your Root File Explorer, as well as a build.prop editor. I used "BuildProp Editor" from the Play Store, but any one off the Play store should do fine.
First, copy your old "cust" folder from your backups into root once again, allowing it to overwrite any identical files.
Now, using the build.prop editor you're going to be looking for 3 lines in build.prop:
- ro.miui.region
- ro.miui.cust_variant
- ro.product.mod_device
Modify the values to be as follows:
- ro.miui.region CN
- ro.miui.cust_variant cn
- Delete the entry "ro.product.mod_device"
Using build.prop editor, hit "select file" and open up /cust/current/cust.prop, and repeat the changes above. Once more, open up /cust/cust/eu/cust.prop and repeat the changes above.
Clear the Themes apps data, and reboot your device. At first it will show you the theme store in English - this is normal. Once you hit "agree" it downloads the Chinese store data.