The Titles of Magical Books in Harry Potter

Blood Brothers: My Life Amongst the Vampires

Simplified Chinese (Mandarin: China)
血亲兄弟：我在吸血鬼中生活 Xuèqīn xiōngdì: Wǒ zài xīxuèguǐ-zhōng shēnghuó	血亲 xuèqīn = 'blood relations, consanguinity'. 兄弟 xiōngdì = 'brothers'. 我 wǒ = 'I'. 在 zài = 'at, in'. 吸血鬼 xīxuèguǐ = 'blood-sucker, vampire'. 中 zhōng = 'among'. 生活 shēnghuó = 'life, to live'.	Consanquinal brothers: I live among the vampires
Traditional Chinese (Mandarin: Taiwan)
血盟兄弟：與吸血鬼同行的日子 Xuèméng xiōngdì: Yǔ xīxuèguǐ tóngxíng de rìzi	血盟 xuèméng = 'blood alliance'. 兄弟 xiōngdì = 'brothers'. 與 yǔ = 'with'. 吸血鬼 xīxuèguǐ = 'blood-sucker, vampire'. 同行 tóngxíng = 'to travel together, move with'. 的 de = connecting particle 日子 rìzi = 'days'.	Blood alliance brothers: days travelling with vampires
Japanese
血兄弟　ー　吸血鬼たちとの日々 Chi kyōdai — kyūketsuki-tachi to no hibi	血 chi = 'blood'. 兄弟 kyōdai = 'brothers'. 吸血鬼 kyūketsu = 'blood-sucker, vampire'. たち tachi = plural marker と to = 'with' (meaning here 'time spent with') の no = connecting particle 日々 hibi = 'days'.	Blood brothers: days with the vampires
Vietnamese (Chinese characters show etymology)
Anh Em Cốt Nhục: Đời Tôi Giữa Những Con Ma Cà Rồng	anh em = 'brothers and sisters'. cốt nhục (骨肉) = 'flesh and blood, blood relationship'. đời = 'life'. tôi = 'I'. giữa = 'amongst' những = plural marker con = classifier, counter for living creatures ma cà rồng = 'blood-sucking demon, ghoul, vampire'.	Flesh-and-blood sisters and brothers: my life among the vampires

For many, blood brothers will suggest old Western TV dramas where the Indian (now known as a Native American) draws a knife and cuts his wrist or finger and that of the white man (always the good guy), places the two together so that their blood mixes, and declares, 'Now we are blood brothers!' This ceremony is less appealing in these days of AIDS and hepatitis B, but the emotional concept of a fraternal bonding between two men of different races or backgrounds still remains.

In this book title, of course, the blood bond is one of a shared taste for human blood, possibly even involving some fraternal sharing of blood from the same victim.

The Taiwanese translator gets this quite right by speaking of a blood alliance 血盟 xuèméng or 'blood alliance'. The Japanese translator does so too. To be honest, I am not sure what the Japanese expression for 'blood brother' is, but the meaning here is clear, not least because 血兄弟 chi kyōdai has the same pronunciation as 乳兄弟 chi-kyōdai, or 'milk-brothers', who are people without a blood relationship who have grown up drinking the milk of the same mother.

The Mainland and Vietnamese translators, on the other hand, incorrectly interpret 'blood brothers' as meaning brothers related by blood.

The word for vampire is the same in the Chinese and Japanese translations, 吸血鬼 (xīxuèguǐ or kyūketsuki) meaning 'blood-sucking demon'. The Vietnamese translator uses ma cà rồng, a blood-sucking creature originally hailing from the mountainous northern regions. The ma cà rồng resembles a Western vampire, with long, tangled hair, long canine tooth, and blood oozing out of its mouth. It is believed to capture children and suck their blood until dead.