I'm fairly sure that is the origin of Erdäpfel. We certainly thought this was a funny name for potato when we learned French in Scotland :-)

When I learned German the word for potato was Kartoffel.

Kartoffel is the standard German word.

Erdäpfel is used in many dialects and has plenty of variants.

Actually the various different words for potatoe and their distribution across Germany, Swiss and Austria is linguistically quite interesting (see this map [1]).

The legend is in German and roughly translates to (from top to bottom):

- Potatoes

- Ground pears

- Earth apples

- Earth pears

- Hearth apples

[1]: http://stepbysteplingue.com/wp-content/uploads/2019/02/karto...

I suppose this "earth apple" formulation coming up in several languages is partly because potatoes are from the New World, and Old World languages won't have a "traditional" word for them. Whereas in English it's basically a loanword.

It also makes more sense when you realize that 1) pomme in older French meant fruit generally, not apples specifically, and 2) sweet potatoes were introduced to Europe well before white potatoes were. So "earth fruit" seems fitting.

Technically apple is also just the general term for fruit from its root in Proto-Indo European, ab(e)l.

Do you have more detail about your second point?

Since they both come from America, sources I can find place them in Europe during the XVIth century.

Diverging but funny: "pommes de route" is a french-canadian colloquialism for horse droppings (on the street - "road apples")

In Chinese one word for potato is "earth bean" 土豆 (the other word is "horse bell tuber" 马铃薯)

Polish is ziemniaki, where ziemia is earth.

So just “of the earth”?

Yes

french fries are pommes frites. the french term is also used in germany (though sometimes shortened to pommes or fritten).

a term falling out if use does not make it foreign. even if no longer common pommes frites is still a french term. the french wikipedia page also does not give any indication that the term is no longer used.