I want to change language via ADB. I try:
adb shell setprop persist.sys.language fr;setprop persist.sys.country CA;stop;sleep 5;start
but I
Your errors have nothing to do with adb. You just lack understanding of how your local shell processes your command. What you are doing is running these commands locally (on your PC):
adb shell setprop persist.sys.language fr
setprop persist.sys.country CA
stop
sleep 5
start
and the error messages you see are from local shell (i.e. there is no setprop executable on your system and start and stop commands have non-optional parameters.
the correct command would be
adb shell "setprop persist.sys.language fr; setprop persist.sys.country CA; setprop ctl.restart zygote"
or in more recent Android versions:
adb shell "setprop persist.sys.locale fr-CA; setprop ctl.restart zygote"