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The letter is fine, but you need to indicate who will pay the cost during the travel (e.g. air ticket fee and the living/food fee, etc.). Because this invitation letter is that you invite your niece to visit you (not to the visa officer), you don't need to translate it into English (the Visa officer knows Chinese well, anyway). If you will pay for the cost, you need to provide the completed I-134 with the support documents (see I-134 Instructions).

By the way, read the following links for extra required document for the minor child travel:
https://help.cbp.gov/app/answers/detail/a_id/268/~/children---child-traveling-with-one-parent-or-someone-who-is-not-a-parent-or

https://help.cbp.gov/app/answers/detail/a_id/1254/kw/1254/sno/1/session/L2F2LzEvdGltZS8xNDM0MTMwNTA5L3NpZC9WT2prcEpvbQ%3D%3D/~/children---child-traveling-with-one-parent-or-someone-who-is-not-a-parent-or