The name German Silver is synonymous with Nickel Silver and is a silver white alloy used mainly to make cutlery and is composed of 60% copper, 20% nickel and 20% zinc but has NO silver content whatsoever other than the very thin electroplating which is sometimes applied to jewellery.
American Silver does not have a fixed silver content like silver in England but is usually produced to the Stirling Silver standard which is 925 parts of silver in every 1000 parts of the total metal (pure silver is very soft and needs some other metal to harden it). In some less costly goods you may also find the 800 in a 1000 fineness being used.
Hope that helps a little as it is a confusing situation.