The recent discussion of how to pronounce "Uyghur", and especially the treatment of the medial consonant, brought up the case of yoghurt/yogurt, which in French is "yaourt" — and today on the Omniglot Blog the Word of the Day is yaourter, "to yoghurt", which is said to be
a French word for the way people attempt to speak or sing in a foreign language that they don’t know very well. Often they mishear and misinterpret the word or lyrics and substitute them with familiar words.
Some of the comments on the Omniglot post suggest that the English equivalent is the noun mondegreen. I've never heard anyone verbing mondegreen, and a bit of web search doesn't turn up much except for the http://twitter.com/mondegreened (which I'm sorry to say belong to someone named "Julian", not "Ed"), and a post on "The mondegreening of America", and a few other things.
But it seems that the key thing about the French word is the nonsense imitation of another language, which is more like a specialization of doubletalk than a verbal equivalent of mondegreen.
There's nothing available from Gallica, nor from wordreference.com, nor from the Dictionnaire de l'Académie Française, so (pending asking Francophone friends) I need to fall back on general web search. And that turns up things like this comment:
Just for the story, in France, when we don't speak English and we want to imitate the sound, we call it "yaourter"(to yoghourt), the imitation sounds like a very nasal language, kind of like a baby crying. It mostly imitates the "cowboy" accent.
Or this one:
Prenez une poignée de bons amis, de préférence des amis aimant chanter, chantonner, fredonner ou même yaourter. Et qui n’ont pas spécialement peur, les liquides houblonnés aidant, de se cramer la honte dans des bars où ils sont pourtant connus. Mettez leur entre les pattes une petite boite carrée pleine de cartes, nommée Shabadabada, et laissez agir quelques heures. Observez le résultat : il semblerait qu’ils alternent des phases de faisage de gueule et d’autres de franche rigolade.
Or again this:
… j'ai rajouté de la super musique dans le lecteur sur votre droite… Playlist à chanter, yaourter, meumeumer, hurler, casseroler aussi!…
These examples do make it seem as if yaourter is a mode of vocal production, with any sense of "slip of the ear" being very much secondary. And it's not clear to me whether imitating the sound of another language is central to its meaning, or if it's rather something more like scat-singing, or sung double-talk, or something like that.
English has a lot of words for speaking or singing nonsensically, but I can't think of any word that refers specifically to nonsensical imitations of the speech of foreigners, although there's a long anglophone tradition of producing such imitations for the amusement of others.