The descriptions of what Pilate had written over Jesus on the cross differs in each Gospel account:
Matthew 27:37
37 And set up over his head his accusation written, THIS IS JESUS THE KING OF THE JEWS.
Mark 15:26
26 And the superscription of his accusation was written over, THE KING OF THE JEWS.
Luke 23:38
38 And a superscription also was written over him in letters of Greek, and Latin, and Hebrew, THIS IS THE KING OF THE JEWS.
John 19:19
19 And Pilate wrote a title, and put it on the cross. And the writing was, JESUS OF NAZARETH THE KING OF THE JEWS.
How do we reconcile all four of the accounts?
First, as is important to understand when dealing with any alleged contradiction in the Bible, but especially in the Gospels, which cover the same events - omitting something is not the same thing as stating that it didn't happen. This is an easy principle to understand, so I won't waste too much time explaining it.
Looking at the part of the superscription that each account mentioned, we can combine them all into a single one:
All of the accounts fit into something like the above being the full superscription.
Also, we know that the superscription was written in Hebrew, Greek, and Latin (Luke 23:38, John 19:20), and so any one of these could be chosen from one of those languages, which may or may not have been a one-to-one match with one another.
In any case, these passages are not a problem. They fall well within the Christian understanding of how the Gospels harmonize, often including differing details that supplement, rather than contradict each other, God-approved paraphrases of what was said, and so on.