I would say that Melkor had from the begining the gift of poetry, since he shared all other gifts - and it may be that he was the most gifted at it:
However, in the same source, it is stated that for ages uncounted the valar (and Melkor) worked together for the actual making of creation. Because, as you quoted, Melkor had from the begining a great interest in language, he may had had time to increase his skill, from Manwe - or even Aule, who is said to have been the most interested in language.

HARRY POTTER plot spoiler alert!!!
 

A similar sort of thing occurs in the Harry Potter series with Lord Voldemort. By splitting his soul into seven pieces he makes his mortal self impossible to kill, but if the Horcruxes containing the six split pieces are destroyed and then his physical body is killed, he gets not even a normal death but is reduced to something less than a ghost, a mere seventh of a shadow of a soul. Pretty much fits the description in Tolkein's letters about what happens to Sauron when the One Ring gets toasted.

We could say that Melkor had the greatest 'gift' of all, the ability to learn. It's also interesting that both he and Aule were notably gifted with language and it was one of Aule's 'followers', Saruman, who was also noted for his 'gift' of learning, and for his skill with language.

Hmm...I like how there's a link between the Smith and the Poet (or linguist at any rate - Poet sounds better though, doesn't it? ;) ), as though craft and language come from the same root. Ties in nicely with what seem to have been Tolkien's own aesthetic values, his fondness for the Arts and Crafts movement (Morris etc).

Even so, all this might be interesting to us, but there's still the very obvious answer that Sauron created the One Ring simply to rule over the other Rings - the clue's in the title of the book, eh? ;) But how did it work? That's where, I think, the issue of Language comes into play, the possibilities of sanwe. Sauron secretly created his One Ring, the Elves secretly created the Three; as soon as Sauron put on the One Ring, they 'perceived' him and removed the Three, and it was never again safe for them to wear these until the One was lost. That must tell us that somehow, the One Ring worked by enabling the wearer to 'see' those who wore other Rings...the Ring, crafted with words, enabled Sauron to break down the barriers of Unwill? This makes for all kinds of interesting questions about whether Hobbit bearers of the One Ring became more powerful than the bearers of the Three, just what Frodo could see in the collective minds of those Three, and how it drove him on...

I am not sure about Melkor's greatest gift being his capacity to learn (well, he could have it, but he forgot about it :D); he gave less heed to the information Eru gave about the Eruhini than even Sauron ; he also failed to see that he can't fight against Eru, even after he is so warned by Eru himself. Oh well - at least His words assure us that even Melkor _will_ see he was only a tool for greater beauty.

I wonder how is it that the bad guys haven't noticed all those things in the Ainulindale which foretold the failure of evil (by and large - or at least that of Melkor in his direct and immediate quest). Melkor himself was too caught up with his own makings; Sauron may have noticed the writtings on the wall, but he later became enamoured of Melkor's power to bring about his plans of organising; perhaps all the rest were from the begining swayed by Melkor and noticed and remember very little.
Apparently, even Frodo is able, theoretically (?), to do such a thing with the one ring:
Interestingly enough, one's unwill may not always work as expected, as we see in the case of Saruman with the palantir:

Well, having a great capacity for learning doesn't necesarily mean you will learn the right things...so speaks one who wasted much of her youthful capacity for learning by having her nose stuck inside Tolkien books! :D I think Melkor possibly thought he was so clever he could find a way round Eru's rules. Yet again this reminds me of Saruman, who believed that superior learning and gathering of ring lore would be the best way to achieve the goal he had been set.

Do you think his arrogance was responsible for this? That he believed he had control and so could outwit Sauron? Or was it something else? One mind cannot 'see' into another if they are using 'unwill', supposedly only Eru can do this. So did Sauron use language with Saruman? Or did he trick him?

You know what they say: all is happy in the best world possible ;). Anyway, may I be permited to note a non sequitur in your statement? Your example is quite the opposite of what you were trying to prove ;).
I don't think he was that stupid - although Tolkien sort of equates (his) evil with stupidity:
If he had the tiniest shred of memory left, he would remember that Sauron had already outwited and outstrenghtened (sp) him, and he did it with a palantir at that.
I don't think Saruman used language either, I guess he was just scared out of his wits by the turnings of the events, which were arranging against his double crossings, that he wanted to have a second opininion through the palantir. I presume that the power Sauron wielded infused the palantir(s) - therefore when Saruman opened (?) his mind in order to direct the palantir to the locations he wanted, he may have unwillingly and unknowingly interacted with Sauron - who may even have directed what Saruman saw, as he did with Denethor.

Oh no, I mean it alright! I ought to have been reading about Hitler or the Corn Laws or somesuch 'useful' learning, which might have helped me get higher exam results but I was, quite literally, 'away with the faeries'... ;)

I agree. Doesn't it say somewhere that the Palantiri did not work through the medium of sound anyway? I am suspicious that they in fact worked in some ways via sanwe. They 'capture' past events which can then be seen, and they do not show 'future' events, but can show current ones, obviously. They can show wider scenes but must be correctly manipulated to achieve this. They also only work in a 'two-way' connection (in that you can only contact one other stone at once - no 'conference calls' :p ); only the stone in Osgiliath could 'see' all other stones. Also, thinking about the way Denethor was trapped unwittingly and eventually driven to despair by it, yet unaware of Sauron's hand/mind, suggests that sanwe had something to do with it, Men having weak skills of unwill.

Indeed, in Unfinished Tales:
I agree - at least this is what we make of Pippin and Sauron's discussion:
(although Pippin is sort of lipsynch-ing- probably due to lack of skill.

I am not sure that Denethor was unknowing of Sauron; he did fight against him and his pull towards Mordor, with great expense of energy (although aided by the fact that he inherited authority).

Voltaire isn't it? Candide to be precise?

Could someone fill me in quickly on what "sanwe" is please?

Interesting thing that bit about Voltaire; I don't know why I thought the phrase belongs to a modern day physicist.

According to the editorial glossary to Osanwe kenta, Enquiry into the Communication of Thought:

Well Voltaire said (or more precisely, the lead character in Candide had a habit of saying) "Everything is for the best, in the best of all possible worlds". You are probably right about some physisist saying it, but I thought it was close enough to Voltaire to have been a slightly mis-worded quote.