Why does the Arkan-thoria have an elvish name?

[Andrettin]

Why does the Arkan-thoria have an elvish name if by far and large it passes through dwarvish/orcish territory?

[zookeeper]

Because... they don't only name places they live in?

There's no particular reason why the elvish name specifically is the most commonly used one.

[Whiskeyjack]

There´s an even better reason: If you go the north route in HttT in "A Choice Must Be Made" Kalenz tells a story of ancient times when the frozen land (where they fight an Orc and find a fiery sword) was ruled by Elves. If you take into account the location of the campaign map this leaves you with the knowledge that the land between the Arkan-thoria and the northeastern end of the Heart Mountains was once Elvish land which was lost to the Orcs.

There you have your reason

Edit: And the mouth of the river (not sure if this is valid, sounds really strange to me, in German we have the perfectly fitting word "Flussmündung") is not that far from Lintanir, thus it is reasonable that the Elves have their own name for it. Kalenz tells that even the humans (who live considerably farther away) have a name for it: Longlier.
Since we are never told the Dwarvish name of it I don´t find it strange that it uses the Elvish name on the map.

[UnwiseOwl]

Just a guess, but I suspect the real reason was turin.
It always boils down to that guy.

[Andrettin]

Because... they don't only name places they live in?

Well, yes, of course, but it's their name that is in general use, despite them seemingly having very little contact with the river.

There's no particular reason why the elvish name specifically is the most commonly used one.

That does seem to be the case though, doesn't it? The elvish name is used by everyone else, even by dwarves themselves. For instance, in "The Council Regathers" (The Sceptre of Fire), Baglur speaks the following line:

"Wait, wait. The gold and coal... I think we can find those in the abandoned eastern mines, north of the Arkan-thoria. Trolls ha’ overrun them, but earlier they were the source of the finest smithing materials."

There´s an even better reason: If you go the north route in HttT in "A Choice Must Be Made" Kalenz tells a story of ancient times when the frozen land (where they fight an Orc and find a fiery sword) was ruled by Elves. If you take into account the location of the campaign map this leaves you with the knowledge that the land between the Arkan-thoria and the northeastern end of the Heart Mountains was once Elvish land which was lost to the Orcs.

There you have your reason

Ah yes, that makes sense, I forgot about that, thanks The Elves being the first inhabitants of the region, it would also make sense that the Dwarves would use their name for the river; plenty real-life analogues exist, such as many European rivers having names with Celtic roots, despite their surrounding areas nowadays being inhabited by peoples who speak Latin or Germanic languages.