It's more of a translation into code than an actual translation issue.

When you complete Vecna by merging its 3 parts, there is a CARDNAME in its text instead of what I presume would be that creatures name showing.
Also, by pressing the right mouse botton while examining The Book of Vile Darkness, Vecna's text is only ''Indestructible''. May be intended, butnot consistent with the final result.

Steps:
1-Have all 3 Vecna's artifacts in play, (Book, Eye, Hand)
2-Merge them to get Vecna
3-Check text.

Screenshots attached.

Have a good day