People, ALLAH uses the word "WE" for himself because:
WE
S1, W1
/wi/ ; strong /wi:/ pronoun [used as the subject of a sentence]
1 I and one or more others: We were all amazed when we heard the news. | Shall we (=you and I) have a coffee, Ted? | Can we (=I and the others) go now, sir?
2 formal used by a king or queen in official language to mean I: We are not amused.
3 used by a writer or a speaker to mean you (the reader or listener) and them: We saw in the previous chapter how this situation had arisen.
4 used especially to children and people who are ill to mean you: And how are we feeling today, Mr. Robson?
5 formal people in general: Do we have the right to destroy the planet?
© Pearson Education Limited 2000
The Excerpt mentioned above is taken from Longman Dictionary of Contemporary English.
If you Christians want to believe that "WE" refers to "THE TRINITY", then I am sorry that is not the case. ALLAH uses the word "WE" because HE is THE CREATOR and has the RIGHT to use the word "WE" for HIMSELF. I mean if the wordly Kings can use it for themselves than why not ALLAH.
And for JESUS, ALLAH has the following to say:
[003] The similitude of Jesus before God is as that of Adam; He created him from dust, then said to him: "Be". And he was.