After I provided ChatGPT with a larger section, the AI appeared to agree with you: 'I'm a lutera—that is to say, I paint mourning paper.' I'll change the translations accordingly. Thanks, boot!

But I think here 'luter' refers to 'Luto', mourning. She converts crds into mourning cards

ChatGPT: For this and the next unit: to make the wordplay more obvious to English readers:

"I'm a luthier."
"And we're Lutherans," said Ido with a grin, delighted to revive that ancient pun, one that had already been used innumerable times.

Translator's note

The Spanish joke works because lutera ("female luthier") and luterano ("Lutheran") begin with the same sequence luter-, inviting a feigned misunderstanding. English preserves much of the effect because luthier and Lutheran are also strikingly similar in sound, although not quite as close as in Spanish.

I think "I'm a luthier." / "We're Lutherans." is the best solution. It keeps the joke brief and lets the narrator's comment ("that old joke") tell the reader that it is intended as a pun.

Lutheran.? Maybe write it "luteran" or just keep "lutera" ?? In the next part, the man wants it to sound like the religion, for a joke, but I think it should be written differently. She uses "lutera" not "luterana".