When I first wrote "Gawain's Guilt-Girdle" (14 lines of verse) I introduced it with a short (modernized/translated) quotation from the Middle English work Sir Gawain and the Green Knight. I think my intent at the time was to point to that original work as source material, to give a feel for the alliterative verse form of that work (which is slightly hinted at in my writing), to establish the setting (archaic and heroic), and to give something of an academic feeling. (Incidentally, the quote might also communicate that the source poem is better, expressing some humility and encouraging people to read that poem.)
Here is how it currently stands:
"This is the band of that blame I bear on my neck,
This is the humbling and the loss that I laugh to have
Of cowardice and coveting that I have caught there;
This is the token of untruth that I am taken in
And I must needs it wear while I may last"
Sir Gawain and the Green Knight
lines 2506-2510 (modernized/translated)
This sash of shame that knights now wear in jest
to little make my failing, strikes its knife
across a heart that feels its heavy blame.
How grave a truth may simple cloth proclaim!
This lively, lady's green recalls that test
of faith and truth, my choice of breath, not life.
Yet knights would make this band a sign of fame.
They mirror shameful marks in light good will
and seek to mend my fault, as one might fill
cracks in a hero's stone with bitter lime.
None but God's blood could kill this evil name
I placed upon myself by lying then--
faithless at last, if better than all men
who walk the earth in this now darker time.
In hindsight I am wondering if the quote should be left untranslated (source):
'Þis is þe bende of þis blame I bere in my nek,
Þis is þe laþe and þe losse þat I laȝt haue
Of couardise and couetyse þat I haf caȝt þare;
Þis is þe token of vntrawþe þat I am tan inne,
And I mot nedez hit were wyle I may last;
(The untranslated form makes it significantly less accessible. The work is not intended as light reading, but it is also not targeted specifically at readers familiar with Middle English. If untranslated, it would be expected that most readers would primarily only gain a sense of archaic language. The untranslated form would be more academic and more accurate as well as more archaic.)
Alternatively, the quotation could be dropped. I am hesitant to simply drop the quote (even though it does not add that much to the writing itself), but I could be convinced that dropping it would be best.
Another concern is that my own modernization/translation is inaccurate and/or inadequately modernized. For comparison here are two competent translations:
"this is the bond of the blame that I bear in my neck,
this is the harm and the loss I have suffered,
the cowardice and covetousness in which I was caught,
the token of my covenant in which I was taken.
And I must needs wear it so long as I live,
(Translator: Michael West; 1898)
"this that I bear in my neck is the badge of this blame.
This is the evil and the loss that I have got
from the cowardice and covetousness that I showed there.
This is the token of untruth that I am taken in,
and I must needs wear it while I may last;
(Translator: W. A. Neilson; 1999 (PDF))
(I seem to recall that I based "humbling" on a note in either a transcription or translation, but "laugh to have" was [I seem to recall] based simply on approximate transliteration and seems to be noticeably incorrect [so should be corrected]. "untruth" is meant in the sense of "unfaithfulness" ("let us be true to our oaths")--more "untroth", like in "betrothed"--but the particular case did involve a lie, so even the modern use would not be particularly inaccurate.)
Providing general guidelines for when an introductory quotation is useful and when such should be translated would make an answer more generally helpful to later readers.