[Phanx]

I'd say it is more harmful than helpful when the addon doesn't actually work in those languages, as Resike mentioned the addon in question does not -- while the users of those sites can read the site where they downloaded the addon, they can't actually use the addon. Those sites also tend to grab whatever version is current when they launch, and then never update, so they end up offering a version that's months or years out of date and doesn't work with the current version of WoW in any language.

Also, if someone on the site is modifying the addon to work in Chinese, for example, not only are they further infringing on the author's rights, but they're also harming all of the users who get their addons from the sites where the author actually hosts it. Their efforts would be better spent submitting their translations and other changes to the author for inclusion in the official version, so that all Chinese players could use the addon, not just the few who are visiting some random leech site.