Who is the Servant God is speaking about in Isaiah 42: 2-4 and 19? Are they the same person?
The Servant in Isaiah 42 is Israel (or Jacob), the nation God chose for blessing but had now fallen into sin and resultant exile. Yet despite haven fallen very low ("thou worm, Jacob") the Servant retains God's steadfast love and will soon be healed. This becomes clear if we look back a few lines, remembering that in the original, there were no chapter divisions. From what is now chapter 41:
Thou, Israel, art my servant, Jacob whom I have chosen, the seed of Abraham my friend. Thou whom I have taken from the ends of the earth, and called thee from the chief men thereof, and said unto thee, Thou art my servant; I have chosen thee, and not cast thee away. Fear thou not; for I am with thee: be not dismayed; for I am thy God: I will strengthen thee; yea, I will help thee; yea, I will uphold thee with the right hand of my righteousness... For I the Lord thy God will hold thy right hand, saying unto thee, Fear not; I will help thee. Fear not, thou worm Jacob, and ye men of Israel; I will help thee, saith the Lord, and thy redeemer, the Holy One of Israel. (8-14)
In the OP's verses from Isaiah 42 the prophet continues in this vein. The Servant, who is still Jacob/Israel, has been wounded but he will not be broken and he shall be restored:
Behold my servant, whom I uphold; mine elect, in whom my soul delighteth; I have put my spirit upon him: he shall bring forth judgment to the Gentiles. He shall not cry, nor lift up, nor cause his voice to be heard in the street. A bruised reed shall he not break, and the smoking flax shall he not quench: he shall bring forth judgment unto truth. He shall not fail nor be discouraged, till he have set judgment in the earth: and the isles shall wait for his law.
Here, the prophet promises that Israel will not only survive the Exile, but will eventually be restored intact, and God's law will be recognized in distant lands.
Verse 19, on the other hand, comes during one of God's laments over his Servant Israel, who has closed his ears and eyes to God's message. The Servant here is the same Jacob/Israel as in the previous verses but is now portrayed as blind and deaf, and God has punished him accordingly. (v.25) But even when the Israel turns away, God's heart toward him does not change:
I will lead the blind in a way that they know not, in paths that they have not known I will guide them. I will turn the darkness before them into light, the rough places into level ground. These are the things I will do, and I will not forsake them. They shall be turned back and utterly put to shame, who trust in graven images, who say to molten images, “You are our gods.” Hear, you deaf; and look, you blind, that you may see! Who is blind but my servant, or deaf as my messenger whom I send? Who is blind as my dedicated one, or blind as the servant of the Lord? He sees many things, but does not observe them; his ears are open, but he does not hear.
But, as the Servant songs often do, the poetry soon turns from judgment to hope in what is now chapter 43:
But now thus saith the Lord that created thee, O Jacob, and he that formed thee, O Israel, Fear not: for I have redeemed thee, I have called thee by thy name; thou art mine. When thou passest through the waters, I will be with thee; and through the rivers, they shall not overflow thee: when thou walkest through the fire, thou shalt not be burned; neither shall the flame kindle upon thee.
The Servant in these verses, indeed in the Servant songs generally, is Jacob, representing the chosen but exiled nation of Judah/Israel. The poetry flows from comfort to judgment, and back to hope again.
Note: Christians traditionally interpret the Servant songs as referring to Jesus. However, when the prophet wrote these words, they referred to the people to whom God had called him to speak, in order to give them hope that their punishment--the Exile--would soon be over.