Historically, most doubts about Greek authorship have centred around Matthew's Gospel. At one stage, Matthew's Gospel was thought to have been written in Aramaic, but this no longer has any serious support. Now, virtually all New Testament scholars and probably even a majority of theologians believe that all four New Testament were written in Greek. The following is a selection of views held by New Testament scholars and commentators.
Uta Ranke-Heinemann says in Putting Away Childish Things, page 218, Matthew's Gospel was originally written in Greek and is not a translation. She says when the Protestant-Catholic “Unity Translation” of 1980 continues to speak about the “old church tradition” of an original Aramaic version, it is refusing to acknowledge the findings of serious scholarship. As John Shelby Spong says in Born of a Woman, page 55, the author's primary language must have been Greek because of his familiarity with the Septuagint scriptures, citing for example, see Matthew’s assumption about 'virgin' in Isaiah 7:14. Similarly, Spong says (page 109) that Luke was written in Greek. Bart D. Ehrman says in Forged, page 227, that Matthew was not written in Hebrew, but in Greek, and was based on our Gospel of Mark.
It would be hard to find anyone who says Mark was not written in Greek. John Carroll says on page 252 of The Existential Jesus that Mark's story was written in Greek. Rhoads, Dewey and Michie say in Mark as Story, third edition page 9, says that Mark's original text was written in Greek.
Among commentators on John's Gospel, Rex Wyler says in The Jesus Sayings, page 275, that scholars presume a Greek original.