In my previous comment I linked to a solution in SO, but here's an alternative (credits: NSHipster[dot]com/simctl): PLIST=~/Library/Developer/CoreSimulator/Devices/$UDID/data/Library/Preferences/.GlobalPreferences.plist LANGUAGE="ja" LOCALE="ja_JP" plutil -replace AppleLocale -string $LOCALE $PLIST plutil -replace AppleLanguages -json "[ "$LANGUAGE" ]" $PLIST