You lost a user manual, you want a translation in another language or you just want to have a look before buying (what I am doing most of the time). You can just download most Nikon manuals in pdf format from the official Nikon sites.
Two things: you need to be registered, that means creating a user on their site and register a Nikon product in your possession, AND, you might need to do that in different countries/regions because sometimes manuals available in Europe are not in the US or the contrary, or you need the Dutch site (the Netherlands) to find an English version of a document, whatever... be prepared to surf a bit before finding exactly what you want.
For French speaking people only, there is a site where you can find old documents not available anymore on a Nikon site. Here is the link to Nikonpassion site.
There are also sites with old repair manuals, spare parts to be found here