Slice string in Go: How can I slice arabic (or other unicode) strings?
First of all, you should really read about strings, bytes and runes in Go.
And here is how you can achieve what you want: Go playground (I was not able to properly paste arabic symbols, but if Chinese works, arabic should work too).
s := "abcdefghijklmnop"
fmt.Println(s[2:9])
s = "维基百科:关于中文维基百科"
fmt.Println(string([]rune(s)[2:9]))
The output is:
cdefghi
百科:关于中文