Luther claimed to Be Isaiah?

Here one from the CARM Christadelphianism forum in which Luther was said to consider himself on par with the Old Testament prophets, considering himself of the same caliber as Isaiah:

Luther interestingly claims himself as "Isaiah", a most excellent prophet:

"Daniel and Isaiah are most excellent prophets. I am Isaiah - be it spoken with humility - to the advancement of God's honor, whose work alone it is, and to spite the devil. Philip Melancthon is Jeremiah; that prophet stood always in fear; even so it is with Melancthon" (Table Talks, Of Gods word, XXIV).

Documentation
The source given is "Table Talks, Of Gods word, XXIV." Despite the incorrect use of the plural, the source is indeed the Table Talk. The version being used appears to be taken from an early English edition of the Table Talk. An earlier English version includes a much broader context, while later English versions edit it down (see for instance, this Hazlitt 1848 edition).

In regard to the German, the text from the early English editions appear to be based on the older German edition of the Tischreden found in Dr. Martin Luthers' sämmtliche Werke, p. 132. The English (bottom of page 91) follows the same content (top of page 129) of the German. One thing the German brings out that the English does not is that the section was not one long Table Talk, but rather many separate statements that the English rendering put together as one context. When one reads the English in this edition, the entire section is headed, On Solomon's Proverbs, but obviously far more is discussed than Proverbs: Esther, Tobit, Judith, Maccabees, etc. The discussion does not flow naturally because it wasn't one natural discussion. These entries were probably put together because they similarly discuss Old Testament and apocryphal books. The Table Talk the quote under scrutiny comes from was recorded by Conrad Cordatus between 1532-1533. The German text indicates it was an isolated statement. WA TR 2 records the statements as 2296a and 2296b (p.410).

Context
The broader contexts located in this English version and this truncated English version  have no bearing on the quote. The isolated quote simply states,

Daniel and Isaiah are the most excellent prophets. I am Isaiah (said Luther, be it spoke with humility) to the advancement of God's honour (whose work alone it is), and to spite the devil. Philip Melancthon is Jeremiah; "that prophet stood always in fear," even so it is with Melancthon. [link]

Conclusion
The Table Talk is a collection of second hand comments written down by Luther's friends and students, published after his death. Since Luther didn't write the Table Talk, the statements contained therein are purported to have been made by Luther and should serve more as corroborating second-hand testimony to something Luther is certain to have written.

Yes, there were times in which Luther spoke of himself as a biblical prophet, but what was his prophecy? It was not the divine forth-telling the future as "thus saith the Lord," but rather the proclamation of the Word of God, not in the sense of new revelation, but the biblical inscripturated Word of God. Lutheran scholar Robert Kolb points out, 

Luther had no illusions about being an Enoch or Elijah returned from the grave…. What counted for Luther- and what linked him in his own mind with Elijah- was the Word of God in their mouths. He was firmly convinced that his tongue and pen proclaimed the same Word of God which Elijah proclaimed. Only because of this could he place himself in the ranks of prophets and apostles. Thus, much of the medieval notion of the prophet was not of importance for Luther. He claimed to possess no special gift beyond the Word which had been present in the mouths of the biblical prophets. His estimate of himself, as constructive promoter of the gospel or as destructive critic of false teaching, was only and only connected with the Word of God” [Robert Kolb: Martin Luther as Prophet, Teacher, and Hero: Images of the Reformer 1520-1560 (Michigan: Baker Books, 1999), p.31-32].

What can we learn from this Table Talk  statement? The statement appears to be a contrast between the personalities of Luther and Melanchthon. Simply do a search on Melanchthon and the word "timid." It's no wonder that one of the main English biographies of Melanchthon is entitled, 

Melanchthon: The Quiet Reformer. In letters to Melanchton, Luther refers to him as "too gentile" (LW 48:257] and that he did not approve of Melanchthon's timidity [LW 48:365]. Or, consider these other purported statements said to be from Luther about Melanchthon:

“Philip stabs, too, but only with pins and needles. The pricks are hard to heal and they hurt. But when I stab I do it with a heavy pike used to hunt boars.” [LW 54:50]

“In the Acts of the Apostles you have a description of us. James is our Philip, who in his modesty wanted to retain the law voluntarily [Acts 15:13–21]. Peter signifies me, who smashed it: ‘Why do you put a yoke on the neck of the disciples’ [Acts 15:10]? Philip lets himself be devoured. I devour everything and spare no one. So God accomplishes the same thing in two different persons” [LW 54:355].

The point of the Table talk appears to be nothing more than a comparison of the personalities of Luther and Melanchthon. There is no corroborating evidence that either Luther or Melanchthon considered themselves to be giving forth extra-Biblical new revelation as modern-day incarnations of Isaiah and Jeremiah.

Luther Believed Prophecy to be Active Today?

This one comes up every so often: either that Luther considered himself a prophet in the Biblical sense of forth telling the future, or that he believed the Biblical gift of prophecy was active in the church of his day. Here's a recent sample from the CARM Christadelphianism board. The person using it appears to think Luther believed in the active gift of prophecy based on a few Table Talk quotes. Here's the first:

Luther believed prophecy to be active today:

"Astronomy, on the contrary, I like; it pleases me by reason of her manifold benefits. General prophecies and declarations, which declare generally what in future shall happen accord not upon individuals and particular things" (Table Talks, Of Astronomy and Astrology, DCCXCVIII).

Context
In regard to the German, the quote was probably taken from a source similar to Dr. Martin Luthers Sämmtliche schriften, Volume 22, 1550. Both sentences are separated by a fair amount of text, including a sub-heading. The first line is "Astronomiam nehme ich an, und gefällt om wohl umb ihres mannigfältigcn Nutzes willen." The second line further down is "Gemeine Weissagungen und Verkündigung, da man etwas insgemein zuvor verkündiget, wie es ergehen soll, reimet noch zeucht sich nicht auf einzelne und sonderliche Dinge und Personen."

This quote as it's been cited in English above was taken from an early English edition of the Table Talk. The version being used appears to be from a later reprint of the Hazlett edition (also found on the CCEL website). The number DCCXCVIII appears to be a later renumbering of the earlier edition. Earlier editions number this entry DCCCXLII.  I'm absolutely certain the quote as it's cited above and found in early Hazlett editions is an edited version of a much lengthier utterance in English from Luther on Astrology. The unedited English can be found here starting at the bottom of page 309. Compare this with other later English editions.


Context

An astrologer and a star-peeper, is to be likened to one that selleth dice, and saith, Behold here I have dice that always run upon twelve; the rest of the fifty casts, they run upon two, three, four, five, six, seven, eight, nine, ten, eleven. Even thus it is with the astrologers; when once or twice their conceit and fantasies do hit, then they cannot suficiently extol and praise the art; but touching the other so often failing, of the same they are altogether still and silent. I accept of astronomy (said Luther), it pleaseth me well for the sake of her manifold profits. David, in the 19th Psalm remembereth the wonderful works and creatures of God in the firmament of heaven, he taketh therein his delight; Job also remembereth Orion, which they call Jacob's staff, the seven stars, &c. To conclude, the example of Esau and Jacob maketh astrology merely a juggling and confounded work, therewith the astrologers always have enough to do to plaster themselves.

Concluding arguments against Astrology. 

First, that doctrine which dealeth and handleth a matter is uncertain; for materia est informis, is without shape and form, without any quality and fitness; the doctrine of the astrologers and star-peepers dealeth and handleth touching matters, therefore astrology is uncertain. Secondly, General prophecies and declarations, when they will declare a thing generally before what in future shall happen, neither do accord nor draw themselves upon singular and particular things or persons; non competunt specialibus & individuis, they agree not to specials and individuals; but the astrologers and star-peepers do teach general predictions and presages which cannot be directed to and upon particular things and persons, therefore the astrologers and star-peepers do wrong, in drawing and directing there predictions to and upon particular and certain persons and things. Thirdly, When at one time many are slain together in a battle, are shot, struck dead, &c. No man can truly affirm, that they were all born under one planet, yet they die altogether in one hour, yea oftentimes in one moment, especially before the mouths of great cannon and ordnances.

Conclusion

Even without the extended context, the subject matter of the truncated quote is about astronomy, not prophecy. I can see though how someone not being careful read the sentences as the separate subjects of astronomy and "general prophecies and declarations." In context, the comparison is between astrology and astronomy, and that Luther rejected the former and was pleased by the later. Then, the second sentence appears in the next section under the concluding arguments. The "General prophecies and declarations" are in regard to that put forth by astrology.