解决方法
将以下文本放在信息属性列表下的键盘扩展名的info.plist中：
<key>NSExtensionAttributes</key>
<dict>
<key>IsASCIICapable</key>
<false/>
<key>PrefersRightToLeft</key>
<false/>
<key>PrimaryLanguage</key>
<string>en-US</string>
<key>RequestsOpenAccess</key>
<true/>
</dict>
<key>NSExtensionPointIdentifier</key>
<string>com.apple.keyboard-service</string>
<key>NSExtensionPrincipalClass</key>
<string>$(PRODUCT_MODULE_NAME).KeyboardViewController</string>