Or I shall live your epitaph to make,
Or you survive when I in earth am rotten,
From hence your memory death cannot take,
Although in me each part will be forgotten.
Your name from hence immortal life shall have,
Though I, once gone, to all the world must die:
The earth can yield me but a common grave,
When you entombed in men’s eyes shall lie.
Your monument shall be my gentle verse,
Which eyes not yet created shall o’er-read;
And tongues to be, your being shall rehearse,
When all the breathers of this world are dead;
You still shall live, such virtue hath my pen,
Where breath most breathes, even in the mouths of men.
Sonnet 81 in modern English
Either I will live to write your epitaph or you will survive my rotting in the grave. Death can’t obliterate the memory of you, although everything about me will be forgotten. Your name will live forever, whereas I, once I’m gone, will be dead to the world. All I will be able to get will be a simple grave but you will be in tombed in everyone’s eyes. Your monument will be my loving poems, which will be read by eyes not yet born, and tongues not yet born will recite them when everyone now breathing in this world will be dead. You’ll live on – my pen has that power – where life is most evident: in the very mouths of men.
Watch Sir Ian McKellen read Shakespeare’s sonnet 81
The 1609 Quarto sonnet 81 version
OR I fhall liue your Epitaph to make,
Or you Å¿uruiue when I in earth am rotten,
From hence your memory death cannot take,
Although in me each part will be forgotten.
Your name from hence immortall life Å¿hall haue,
Though I ( once gone) to all the world muſt dye,
The earth can yeeld me but a common graue,
When you intombed in mens eyes Å¿hall lye,
Your monument ſhall be my gentle verſe,
Which eyes not yet created Å¿hall ore-read,
And toungs to be, your beeing ſhall rehearſe,
When all the breathers of this world are dead,
  You ſtill ſhal liue (ſuch vertue hath my Pen)
  Where breath moſt breaths,euen in the mouths of men.
See the British Library’s 1609 Quarto.
The meaning of the original is perfectly clear. There is no want of a cumbersome and patronising version in “modern English”.