Fully sharpened double-edged knives are NOT illegal to sell, buy, own, or OPENLY carry according to California state law. California state law only mentions "dirks and daggers" as a generic term for "concealed stabbing weapon". California penal code 16470 specifically defines a "dirk or dagger" as "any item, with or without a guard, that is capable of ready use as a stabbing weapon". And even then such language only pertains to CONCEALED CARRY.
There is no mention of double-edges, or single-edges, or false edges, in California state law. Many items, even ones with NO edges, qualify as "dirks and daggers" under California law, including but not limited to - sharpened screwdrivers, icepicks, folders carried in the open and locked position, homemade shanks, etc. Basically, any item carried CONCEALED and capable of being used as a stabbing weapon.
Many stores here in California sell fully sharpened double-edged knives and daggers (I've bought several here), and it is completely legal under Ca state law to OPENLY carry double-edged knives. I know this because my lawyer explained the law to me in detail. I've carried fully sharpened double-edged knives openly on several occasions without concern here in San Diego.