They had heard French spoken and German.

Aunt Emma knew German, and used to sing a song about bedeuten and zeiten and bin and sin.

Nor was it Latin.
Peter had been in Latin for four terms.
It was some comfort, anyhow, to find that none of the crowd understood the foreign language any better than the children did.
"What's that he's saying ?" asked the farmer, heavily.
"Sounds like French to me," said the Station Master, who had once been to Boulogne for the day.
"It isn't French!" cried Peter.
"What is it, then ?" asked more than one voice.

The crowd fell back a little to see who had spoken, and Peter pressed forward, so that when the crowd closed up again he was in the front rank.
"I don't know what it is," said Peter, "but it isn't French.

I know that." Then he saw what it was that the crowd had for its centre.