For the first several months after their exile back through the wardrobe, Edmund developed a habit of cornering one or another of his siblings and pointing out various oddities about Narnia and their experience there, which he had only noticed since their return to England. Peter and Lucy listened patiently enough at first, but eventually they began to insist that he should simply accept that their two worlds were different and that they had doubtless thought differently in Narnia as they adapted to that land. Finally, only Susan was left to bear Edmund's philosophical ambushes.
One windy afternoon, he crept up on her in the library and startled her into reaching for a nonexistent bow when he cleared his throat. "Make some noise when you walk!" she scolded him, before looking back down at the poem she'd been reading. She rather liked Yeats; he was romantic and just a touch wild, which suited her mood these days.
"My apologies," said Edmund, not sounding particularly contrite. "Sister, have you considered the oddest contrast between England and our former domains?"
"How you can single one incident from the surfeit of oddity surrounding us is beyond me," she said, closing the book and setting it beside her on the sofa. "But tell me your thoughts."
"That's just it," said Edmund. "Did you listen to yourself? I reminded you of Narnia, by word and by phrasing, so you slid into speaking as a queen instead of a schoolgirl. But we're still speaking English, and we spoke English in Narnia, too."
"I don't see--" Susan began, and then frowned. "So we are and so we did, brother," she said, more slowly, the minor formality smooth on her lips. The phrase sounded out of place somehow, or maybe it was the change in her voice, ringing suddenly clear and silver in the dusty air of the Professor's private library. "What of it?" she continued, deliberately setting aside years of a life she would never be able to reclaim. "It's odd for different worlds to use the same language, especially when English is such a hodgepodge, but how is that any more odd than Talking Beasts and enchanted winters?"
"I suppose it isn't any more odd," Edmund said, glancing reflexively upwards toward the attic room that held the wardrobe. "But that's not quite my point. What strikes me as most peculiar is that every other land in that world, so far as we ever knew (and I, for one, knew quite a lot about our neighbors, no matter how distant) all of them spoke English. Oh, some had a bit of local flavor here and there, mostly to do with titles or proper names, but the basic words and grammar were identical. So was the writing. It's as if everyone from Scotland to China spoke the same language -- French, say -- even amongst themselves."
Susan's frown deepened. "You're right. Even the Calormenes spoke English, for all that they despised Narnia. Still, what of it?"
Edmund shoved his hands into his pockets and shrugged. "Nothing, really -- it struck me funny just now, that's all. And I wondered why I never noticed while we were still there. It's as if that was simply the way of the world, and having more than one language would be ridiculous as well as impossible. Now, of course, having only one language seems unlikely at best."
"No more unlikely than our going to Narnia in the first place," said Susan, tiring of the subject. Peter and Lucy had the right idea: while they were in England, it was best to focus on England. Within certain limits, of course -- there were some things too important to forget. And speaking of those... "Perhaps you should ask Aslan, if we ever see him again."
Edmund agreed that this was the best plan of action, but by the time they next saw the Lion, he had other things on his mind.