|蛇佬 shélǎo =
腔 qiāng = 'speech'.
|爬 pá =
說 shuō = 'to speak'.
語 yǔ = 'language'.
|Crawling speak language|
|パーセルタング Pāserutangu = Parseltongue||Parseltongue|
||xà (蛇) = 'snake'.
ngữ (語) = 'language'.
Parseltongue is the language of snakes, which sounds like hissing to people who don't understand it. Knowledge of Parseltongue is a rare talent, one which Harry had only because Voldemort unintentionally shared part of his soul with him.
Chinese (Mainland): The Chinese name literally means 'snake language', but the words used carry deeper connotations that are hard to convey in English. The most straightforward word in the whole expression is 蛇 shé meaning 'snake'.
The second character is 佬 lǎo, a pejorative term that means something like 'guy'. It's used in expressions like 闊佬 / 阔佬 kuòlǎo moneybags, 外國佬 / 外国佬 wàiguólǎo foreigner, and 鄉巴老兒 / 乡巴佬儿 xiāngbalǎor country bumpkin. The best known example, of course, is Cantonese 鬼佬 (guǐlǎo in Mandarin pronunciation), conventionally translated as 'foreign devil'. So 蛇佬 shélǎo is a rather unflattering term for snakes.
The third character is 腔 qiāng. The basic meaning is 'cavity', as in 口腔 kǒuqiāng 'oral cavity'. However, it has the further meanings of 'tune, speech, tone, accent'. Among the many expressions formed using 腔 qiāng are 打官腔 dǎ guānqiāng 'to speak like a bureaucrat' and 京腔 jīngqiāng 'Beijing accent'. It's used to refer to a 'way of speaking' rather than 'a language' in the ordinary sense.
Thus 蛇佬腔 Shélǎo-qiāng actually means 'the tones (manner of speaking) of a snake guy', in a somewhat derogatory sense. It is by no means a neutral term like 'snake language'.
Chinese (Taiwan): The Taiwanese translator uses 爬說語 Páshuō-yǔ. The first character 爬 pá means 'to crawl' or 'creep'. The second 說 shuō means 'to speak'. The third character, 語 yǔ, means 'language'. Literally this means 'crawl speak language', which sounds like a language you speak while you are crawling. This is a reasonable enough explanation of the language a snake might speak.
In fact, the Chinese word for 'reptile' is 爬行動物 / 爬行动物) páxíng dòngwù 'crawling animals'. Thus the use of 爬 pá 'crawl' here to describe snakes is quite natural.
But more importantly, the Taiwanese translator is also attempting to capture the sound of English 'parsel' with the expression 爬說 páshuō. That is 爬說語 Páshuō-yǔ not only means 'crawling (or reptile) talking language', 爬說 páshuō also sounds something like English 'Parsel'.
Japanese: The Japanese translator is the least imaginative of the lot. The name Parseltongue is simply transliterated into Japanese as パーセルタング Pāserutangu. There are no connotations at all for a Japanese speaker, merely the knowledge that it is an English word.
Vietnamese: The Vietnamese translator uses words meaning 'snake language'. In everyday Vietnamese, 'snake language' might be expressed as tiếng rắn, but this would be too pedestrian for 'Parseltongue'. Instead, the translator turns to the fancier Chinese-sounding expression Xà ngữ (in Chinese characters 蛇語 / 蛇语).
This elevates the tone of the name into something altogether more lofty and mysterious. Chinese roots in Vietnamese perform a similar function to Latin roots in English. Using Chinese-based vocabulary is akin to saying Serpentilingua in English, with a fancy Latin-style name instead of a plain word like 'Snake-tongue'. (Note: the author does not guarantee that Serpentilingua is a well-formed Latin word!)