How does Shakespeare's use of language in Act 3, Scene 1 of The Merchant of Venice portray Shylock's villainous side?

In act 3, scene 1, Shakespeare's use of language, within the context of the conversations that make up this scene, establish the depth and intensity of Shylock's vengefulness. While his vengeance is most notably aimed against Antonio (who is the main target of his resentment), in this same scene we see it aimed at his own daughter after she has run away with Lorenzo, robbing him in the process. Thus, in his conversation with Tubal, Shylock wishes her dead with a striking bit of imagery, stating:

I would my daughter were dead at my foot, and the jewels in her ear! would she were hearsed at my foot, and the ducats in her coffin!

This image, of his daughter buried together with his jewels, with both restored to the waiting Shylock, powerfully showcases both his materialistic greed and intense resentment and desire for vengeance, both intertwined with one another.

Of course, as we see in the case of Shylock's bond, ultimately, his desire for vengeance tends to trump his desire for wealth. When Tubal speaks about Antonio's economic distress, Shylock expresses glee at the very thought, stating: "I'll plague him; I'll torture him; I am glad of it," a reaction that does contain some element of situational irony to it. Antonio has borrowed heavily from Shylock, and, with that in mind, you would expect a lender to be upset by this kind of news, but Shylock's delight in the face of his own financial loss is a powerful expression of the depth of his malice towards Antonio himself.

However, the most famous moment in this scene occurs before these interactions with Tubal, in Shylock's famous "I am a Jew" speech. This moment, too, is shaped by an ironic reversal, as Salerio (speaking about Shylock's bond with Antonio) states his assurance that Shylock will not take his pound of flesh, asking "what's that good for?" To Salerio and Solanio, calling the bond amounts to insanity, but Shylock is quick to correct them otherwise.

His speech expresses the depths of his resentment and rage not only at Antonio, but the entire Christian society in which he lives and the anti-Semitism they exhibit against him. To achieve this dramatic effect, Shakespeare utilizes parallelism and a strategic repetition of that parallel structure. See, for example:

Hath not a Jew eyes? Hath not a Jew hands, organs, dimensions, senses, affections, passions? Fed with the same food, hurt with the same weapons, subject to the same diseases, healed by the same means, warmed and cooled by the same winter and summer, as a Christian is? If you prick us, do we not bleed? If you tickle us, do we not laugh? If you poison us, do we not die? And if you wrong us, shall we not revenge? If we are like you in the rest, we will resemble you in that.

With this speech in particular, Shylock's characterization transcends his role as villain to become a three-dimensional personality with heavy emotional scars and trauma, seething in pain. At the same time, however, these lines carry with them an extraordinary degree of versatility in terms of how they can be delivered. You can imagine a composed, dignified Shylock voicing these lines with a tone of sorrow, or you can imagine Shylock angry, even raging at these circumstances. In all cases, however, these lines humanize Shylock, providing the perspective from which his villainous quest for vengeance arises and the conditions that have shaped him into the vengeful antagonist he has become.

How does Shakespeare's language link Shylock to murder in The Merchant of Venice?

An interesting question. I'd say Shakespeare does this both through language used by Shylock and language used by others to describe him. When Shylock is talking about eating with Christians (Antonio), he refers to eating pork as being where the demons were cast. When he discusses Antonio, he flatly states his hatred, and plans to take a "pound of flesh." That's a lot of flesh, and if taken near the heart, would make him a murderer. He repeats this desire, and calls for vengeance even over money in Act III.

As far as what is said about him, the way Antonio talks about him in Act I makes him sound evil, and in Act III Antonio flatly states " He seeks my life."
Greg