translatewiki.net find people who object to participating because "it is not a WMF project". In the case of translatewiki it should by now be obvious why they should; it provides an essential service to the development of MediaWiki.
At translatewiki.net we internationalise and localise the software that is developed elsewhere. The software gets a quality check before the community starts localising and the localisations get a quality check before we commit it to the relevant source repository.
When our community does it work well, nothing changes except for the languages a message is available in. Translatewiki is part of the Wiki movement together with many project outside of the WMF that have their own niche and are worthwhile in their own right. Translatewiki is one, OmegaWiki, Wikia, Wikihow ..... the list goes on.