回复：朋友翻译英文，通晓中英文的声明签字用公证吗？

I would still do the notarization. I did it for my daughter's birth certificate to apply for H-4 and recently again for her I-485. 

It took me half an hour and $5 only to get the mind peace. I took my friend to a local public notary so that 

my friend signed right there on the certified letter (including her address and contact infor). Then the notary person pressed his seal on the letter.