用这个习惯用法declare the commencement of ...表示“宣布。。。开幕”
为了表示礼貌/显得正式，可以说
Now it's my great honor to declare the commencement of ...International Conference.
或者： I hereby declare the commencement of ...International Conference.
Now I declare the XXX meeting/conference formally begins.
I think it's alright.
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