The only place where 'Greeks, Latins, Celts and Germans' suddenly show up is in 1950's (and earlier) literature. ;) These days we've pretty much stopped talking about Celts and Germans all together. NW European Prehistory is more focussed at regional differences than 'grand narratives' which talk about the rise of peoples such as celts or germans (although I have to note that archaeologists in Germany and Scandinavia take a bit more of a conservative standpoint towards these topics).

Taking the celts as an example, most parts of what we associate with 'Celts' can be lead back to the La Tene and before that the Hallstatt groups in Central Europe. Aspects of Hallstatt material culture can be found replicated elsewhere, for instance in the Southern Netherlands. However rather than exactly copy Central European objects and practices, they incorporated Hallstatt burial customs (and possibly parts of the belief systems that go along with them) in their own burial customs. So we're not really talking about a 'people', or 'culture' but about groups of peoples who shared some aspects of their everyday lives and differed in others.

Archaeologists who interpreted these groups as 'celts' emphasized the shared aspects of life to intepret culture-groups that were more or less comparable in where they were located to modern day nation states. As you might guess, this says more about the ideals of those nation states than about prehistory.

If you're interested in this stuff I can recommend a chapter by John Collis from the book Prehistoric Europe: theory and practice.