For those of you in the Know, (and you Know who you are) this is the definitive answer to that question that everyone who is a fan of John Boorman's "Excalibur" has always wanted to know.....
The mystery of Merlin's Charm of Making is, alas, no longer a mystery.Although Merlin and Morgana both pronounce things differently from each other, and even Merlin has two sounds which to me sound like phonemes but which must be allophonic, I get the following from the Charm of Making in John Boorman's film Excalibur:
/a'na:l naθ'rax, u:rθ va:s be'θud, dox'je:l 'djenve:/
It's certainly not Welsh. It looks very much like an attempt at Old Irish. (One wonders where Boorman got it.) Following is the best I can do at reconstructing reasonable Old Irish from it. It is probably a defective reconstruction. I have normalized to Modern Irish orthography to indicate lenition.
In Old Irish Anál nathrach, orth’ bháis’s bethad, do chél dénmha In Modern Irish: Anáil nathrach, ortha bháis is beatha, do chéal déanaimh
In English: Serpent's breath, charm of death and life, thy omen of making. anál nathrach = breath of serpent orth’ bháis ’s bethad = spell of death and of life do chél dénmha = thy omen of making anál fem. -á stem 'breath, breathing' nathair fem. -k stem 'snake, serpent' g. sg. nathrach ortha fem. -n stem 'prayer; incantation, spell', from Latin oratio bás masc. -o stem ‘death’ g. sg. báis ocus conj. ‘and’ here shortened to 's betha masc. -t stem ‘life’ g.sg. bethad do prn. ‘thy’ Usually unstressed cél masc. -u stem ‘omen, augury, portent’ dénumh masc. -m stem 'making, doing' g.sg. dénmha
Modern Irish would have the -is in bháis as a /sh/ sound, but it might not have been so palatalized in the Old Irish period; and the nonpalatal ’s of ‘and’ ought to reinforce that. The third part of the charm could also be dochél dénmha 'an evil omen of making', but that suits the sense badly. The word do ‘thy’ is usually unstressed in speech but what can you do... Note that Merlin says dénmhe, which ought to be dénmha; perhaps there is some sort of 'incantation register' in which a final vowel can be altered in this way.... In any case, I am less than happy with the third part of this. I'd like to have seen an imperative or hortative, but verb-first syntax precludes even dénae, the imperative of do-gní (from which the verbal noun dénumh is formed), which anyway doesn't have the nominal formative -mh.
I would be interested in hearing from specialists in Old Irish as to their opinions of this. There are other possibilities for the retro-translation, and indeed the use of a Latin loanword, given the context, is problematic.
(credit to Michael Everson for this masterful investigation!