When Filch's cat, Mrs Norris, is found petrified at Chapter 9 of The Chamber of Secrets, the enraged Filch accuses Harry of the crime. Filch is particularly distraught that Harry knows he's a Squib. A Squib?
It's only a couple of pages later that we find out what a Squib is: Someone who was born into a wizarding family but doesn't have any magic powers.
In the Taiwanese version, Filch's accusation runs:
'See what he wrote on the wall! He found -- in my office -- he knows I'm a -- .... He knows I'm a 'firecracker'!'
Why Filch should be upset at being a 'firecracker'? The firecracker referred to in the Chinese, 爆竹 bào-zhú, is a string of small noisy crackers that is let off on special occasions like weddings, New Year, etc.
The problem with the Taiwanese translation seems to result from an over-reliance on dictionaries. 'Squib' does indeed mean 'firecracker' in English, generally of the smaller variety. That's how it's defined in English-Chinese dictionaries.
For speakers of the British variety of English, however, 'squib' is more often used for a firecracker that goes off with a fizz rather than a bang. Indeed, the only time many English speakers come across the word 'squib' is in the expression 'damp squib' - a dud firecracker. In other words, the first impression that a (British) English speaker would get is that Filch is a disappointment or a dud. This impression is confirmed by Ron's explanation later on.
For many American speakers, however, the impact of the term 'squib' is more problematic. Americans may be more familiar with the squib as technical term in Hollywood, where it refers to a small pyrotechnic device used to simulate a bullet strike in making movies. An electric ignitor makes it go off on cue, blowing a hole in a person's clothes, possibly bursting a fake blood bag, etc. It is also used for vehicles, etc. (Thanks to Terry Hancock for pointing this out).
At any rate, by translating 'Squib' as 'firecracker', the Taiwanese translator achieves exactly the opposite effect of that which Rowling intended, making Filch sound positively peppery!
The Mainland version translates 'Squib' as 哑炮 yǎ-pào, a shell that fails to explode i.e., a dud. This is much closer to the intended meaning.
If we look at the Japanese version we find the meaning is conveyed in a different way. Filch's words are (translated literally): 'You read the words he wrote on the wall! He saw -- in my office -- he knows. I'm... I'm... ... He knows I'm a defective sukuibu'.
Rather than find a Japanese equivalent for 'Squib', the translator simply uses the English word sukuibu, written スクィブ. The brief explanation deki-sokonai no ('defective' or 'failed') is added in front because sukuibu is as much of a mystery to Japanese readers as it is to us when written like this.
This method of translation is effective in conveying both the meaning and pronunciation of the English term. However, it does have its drawbacks:
1. 'Squib' is an actual English word, not a made-up term like 'Muggle'. Since Harry Potter in Japanese is already packed with transliterated words from the English original, importing 'Squib' runs the risk of overload.
2. The explanation makes the translation somewhat verbose. In particular, the explanatory deki-sokonai 'defective' in Filch's speech is a tad unnatural and weakens the dramatic effect. Filch is hardly likely to go out of his way to clarify to all present what a 'Squib' is; he's already distraught enough that Harry knows about his weakness.