I have to write a sales pitch about an invention but I have to be Othello. What kind of language should I use?

What a creative assignment! I am assuming you already know what product that your sales pitch will be about.  So, I will try to help you with Othello's language.  Look at Othello's early speeches and then again at the end of the play, in Act 5.  Othello's speech is different from other characters in his frequent use of natural imagery and references to war.  For instance, he speaks of the feats of "broil and battle," and 

antes of vast and deserts idle,

Rough quarries, rocks, and hill whose heads touch heaven.  (Act 1, scene 3)

Othello also tells stories or anecdotes. He likes to tell an "unvarnished tale."  For instance, when asked how he and Desdemona fell in love, he narrates the story of his meetings with her, his telling her of his adventures, and her reactions.  Even in Act 5, when Othello gives a speech before he kills himself, he tells a story of a "malignant and turbaned Turk" whom he executed. In each of these stories, Othello's language is eloquent but simple. His sentences can be long, but they are often compound sentences rather than complex.  He is direct and forthright, without irony or puns.  It is only when he is under Iago's influence that his language changes to include animal imagery, puns, and sarcasm.  

Othello likes to use hyperboles to express his strong emotions:  

Excellent wretch!  Perdition catch my soul

But I do love thee!  (Act 3, scene 3)) 

and

Oh, that the slave had forty thousand lives! (Act 3, scene 3)

And for emphasis, he interjects his speech with such exclamations as "Zounds" and "Death and damnation" and "Oh!" Other favorite words are "monstrous," "horror," "perdition,"  "foul." Another speech characteristic is repetition.  Note how many times he repeats "handkerchief, " for instance.  And, you can't go wrong if you incorporate several alliterations within your sales pitch, such as "mighty magic" and "flood and field."  

Remember that Othello is passionate and powerful.  If he loves something or someone, he loves with intensity and hates with equal intensity.  He prefers actions to words, and he does not joke around.  

Good luck with this assignment.