Did Rashi mean Canaanite?

Devarim 3:9

:צידנים יקראו לחרמון שרין והאמרי יקראו−לו שניר

"Sidonians would refer to Hermon as Sirion, and the Amorites would call it Senir" (Artscroll)

On this verse, Rashi comments:

:שניר − הוא שלג בלשון אשכנז [שנעע] ובלשן כנען

Rashi explained that senir, שניר means שלג, snow, in the languages of Ashkenaz and Canaan.

Although Biblical Ashkenaz wasn't Germany, it is obvious that לשון אשכנז means German, for in Rashi's day Germany was called Ashkenaz. As discussed here, in Rashi's time Canaan reffered to the Slavic and Baltic territories. So Rashi is saying that Biblical "senir" is similar to the old German and Slavic words for snow, which Rashi transliterates as שנעע, s-n-'-' (roughly, snow).

How does Artscroll translate the words "לשן כנען"?

Canaanite. Rashi is saying that "senir" is "snow" in the German and Canaanite language.

How did Rashi know the Canaanite language? What was the Canaanite language?

The answer to the second question is, roughly Biblical Hebrew (see Isa. 19:18 שפת כנען and related commentaries, also see related). If so, that certainly answers the first question, since Rashi did know Biblical Hebrew! But that isn't what Rashi is talking about at all. It would be like assuming that ancient Italians spoke Pig Latin.

The Judaica Press Tanach with Rashi translatesmore or less correctly (even if using 19th century lingo) as "Slavish," citing Abraham Berliner (1833-195) who published the first critical edition of Rashi in 1866. Who is responsible for the Judaica Press Tanach with Rashi? Rabbi A.J. Rosenberg. Who is Rabbi A.J. Rosenberg? He has worked extensively for Artscroll, putting out many editions of their Yad Avrohom Mishnayos.

If an Artscroll associated rabbinic scholar plainly knew how to translate לשן כנען then why the error in Artscroll's edition? Clearly this isn't esoteric maskilische knowledge.

For what its worth, the same error can be found in the Metsudah Chumash with Rashi.

So here's the question: why did Artscroll get it wrong? Metsudah is a solitary enterprise, although I assume R. Avrohom Davis has his works peer reviewed. Artscroll is a huge company with dozens of writers. Is it simply a case of one hand not knowing what the other's doing? After all, in addition to being an entity, Artscroll is also composed of hired writers of varying ability and quality. Is the sort of maskilische knowledge and source that A. isn't desirous to incorporate or cite? As will be shown in future posts, A. has an uneven record on this regard.