It's because of the pan-Canadianist pretense that because BC is a province of Canada, it should have a bilingual name (why this is done for the Latin "Nova Scotia" into French, when we don't say "New Scotland" in English, is another matter); I agree with you and I think once-upon-a-time removed the French, but I guess it's back.  There's a certain lexical irony/injustice in the French translation, too, because the "Columbia" part of the name comes from the river (via the fur district named after it), not the country (i.e. Columbia as the poetic name for the US, with nothing to do with Colombia except the shared namesake); the river got its name not from the poetic name of the US, but from Capt. Gray's ship The Columbia, which was the first to enter and sail up the river (so 'tis claimed); and the ship was named for the US, by way of its poetic name.  Confusing, huh?  Yeah, but the upshot is that in French the name of the river is la fleuve Columbia, but they insist that BC's name in French should be la colombie-brittanique i.e. from la colombie, which is the name for the South American country.  This is not just bad history of course, it's downright incorrect; The Columbia portion of the We are expected to use accents on Montreal and Quebec when writing English; they can't even be bothered to get our name, and its history, right.  "They" includes me, by the way, as I'm 1/4 Franco-canadien and, for someone born in BC, speak it pretty well (from my own initiative, not from family background).  Anyway, in a historical/lexical sense the French name SHOULD be la colombia-britannique"; the clincher would be in any historical French-language HBC or NWC documents referring to the Columbia Fur District in French, i.e. as to which form they used; not that anybody in l'office de la langue francaise or the academie francaise'' gives a ****.  My two bits, and what-for.