When you start up a Mac while holding down Command-R on the keyboard, the Mac boots into macOS Recovery. In this mode, you can run Disk Utility, access the command-line Terminal app, and reinstall the operating system. But what do you do if you restart your Mac into Recovery mode and a language appears other than one you know?
This doesn’t seem to happen at random, but it can occur when you’ve purchased a computer from someone who installed the system using another language, which can remain in place in the Recovery partition, a separately organized part of your startup drive.
Fortunately, there are a few ways to resolve this.
Read more at MacWorld.com