Now filing I-485 but cannot read English, who signs the form I-485 Part 5 & 6

I agree with the other lawyers, he must sign for himself.

If you or someone else is helping to interpret the questions on the form, then under Part 5, he must sign under the section that says the questions have been translated for him. Under that same section, you must sign under the part about the interpreter. Under Part 6, you should also sign if you helped prepare the form on his behalf.

He must sign after everything has been translated for him.

He does.