It occurred to me that omes wrote in gmane.os.netbsd.documentation:
> It's about beeing able to chose to read docs in your native language,
> simply because some people are more comfortable with that.

Just my two cents, and why I usually prefer English/original documentation
over a translation:

1) Translations are risky, especially when done by somebody else, since it
   depends on the translator to fully understand the subject. If the 
   translator isn't comfortable with it, the translation may end up being
   misleading or confusing. The original document is often a more reliable
   source of information. This is increasingly true if the document at hand
   deals with intricate details or complex concepts.
2) Consistency, or the lack thereof. Localised documentation only makes sense
   if you can guarantee that it offers the same information than the original,
   and that it will get updated accordingly. This is often not the case. Take
   Wikipedia, for example. Quite often, the various localised versions offer
   completely different texts and different information, often mutually
   exclusive. The Dutch article about binary prefixes claims that the IEC
   introduced the new-fangled kibi-, mebi, gibi etc. prefixes in 1998. The
   rest claims that it was in 1999. The Dutch, Norse, Portugese, Slovak and
   Czech versions claim that there's no equivalence to Zetta (1E21) and 
   Yotta (1E24) because they're meaningless for practical use, all other
   versions claim their existance (zebi and yobi, respectively). I know
   that this says more about wikipedia than it really says about nationalised
   documents, but it *is* indicative of the errors and differences you can
   get.
3) The necessity also depends on the target audience. A basic "how to configure
   a NAT box" might be worthwhile to translate, if your target audience is
   likely to be less comfortable with English. A deep and detailed discussion
   about the inner workings of pf might be a different issue; most people
   wouldn't be interested in it, and those who are are usually quite capable
   of reading English. Furthermore, the two points I made above are more of 
   an issue here. However, this is probably a bit of a national issue;
   from my own observation, I'd say that German and French people are more
   likely to appreciate a translated document than a Dutch person. 

I don't want to suggest that I'm opposed to all kinds of documentation being
translated - I'm not. It makes sense to translate installation guides, and 
maybe the first few chapters of the NetBSD guide, but once things get 
technical I'm not so sure if it's worth it.