This policy setting allows you to turn off Open Extended Dictionary.
If you enable this policy setting, Open Extended Dictionary is turned off. You cannot add a new Open Extended Dictionary.
For Japanese Microsoft IME, an Open Extended Dictionary that is added before enabling this policy setting is not used for conversion.
For Simplified Chinese Microsoft Pinyin, an Open Extended Dictionary that is added before enabling this policy setting is still used for conversion.
If you disable or do not configure this policy setting, Open Extended Dictionary can be added and used by default.
This policy setting is applied to Japanese Microsoft IME and Simplified Chinese Microsoft Pinyin.