Because Melinda and I just had a conversation about this:
- Alces alces – AmE: moose; BrE: elk (mostly); DE: Elch; FR: élan or orignal. The word moose seems to be borrowed from an Algonquian language, while elk is a cognate of alces and many other names in Germanic, Slavic languages as well as Greek. The etymology of the French words is surprisingly complicated (I’m reading about Basque for orignal and Lithuanian for élan — to be confirmed!).
- Cervus canadensis – AmE: elk or wapiti; BrE, FR: wapiti; DE: Wapiti or Wapitihirsch. _Wapiti_ is from a Shawnee or Cree word. German speakers who don’t know the correct name would sort this one under Rothirsch.
- Cervus elaphus — EN: red deer; FR: cerf élaphe; DE: Rothirsch. This is the animal European German speakers think of when they say Hirsch, or the French when they say cerf — the prototypical deer of the continental European forests. The American elk (wapiti) was believed to be a sub-species of this (apparently incorrectly), and would be naively considered as a large red deer by Europeans.
- Dama dama — EN: fallow deer; FR: daim; DE: Damhirsch. Apparently introduced to Europe from the Middle East/Western Asia as a huntable deer species by the Romans.
- Capreolus capreolus – EN: roe deer; FR: chevreuil; DE: Reh. The Latin/scientific and French words make me think that for some time the animal was grouped with goats.
In German, the general term for a member of the deer family (Cervidae), of which all of the above are members, is _Hirsch_. Colloquially, a red or fallow deer, or a member of a non-native species such as a Sitka deer, wapiti or white-tailed deer would be referred to as a generic Hirsch, but a roe deer would be a Reh and a moose/elk an Elk. I’ve heard young Germans refer to an image of a Chinese water deer as _Säbelzahnreh_ (saber-toothed roe deer).
When I was a child, seeing roe deer on a drive through the countryside was a moderately rare treat. Very very occasionally you might spot a red deer. The question “War das ein Reh oder ein Hirsch?” was common, and it’s hard to translate because English has no word for deer that excludes the roe deer. So you might go for something indirect (“Was this a roe deer or some other kind of deer?”) or, better, for something more specific depending on what other kinds of deer would be around (“Was this a roe deer or a white-tail? a roe deer or an elk? a roe deer or a moose [um, these two are hard to confuse]?).