Pre-conversion European belief systems had a lot of local spirits and drew heavily on nature as an obvious habitat for all sorts of entities and powers. I would be extremely cautious about asserting that Celtic beliefs were dramatically different in this regard from those of the Germanic world. Besides the question of what those terms mean - "Celtic" and "Germanic" cover a lot of geography and many periods (see the comment by /u/Airgialla) - finding dramatic distinctions might be very difficult. There were, for example, considerable similarities shared by Scandinavian and Celtic pre-industrial folklore and belief systems, so it is easy to imagine that the same might have been true before conversion.

Neo-Pagans have found it useful to emphasize both beliefs and practices associated with nature as well as anything associated with the Celtic world. The modern inclination to lean in this direction should not be taken as an indication that there were distinctions along those lines "between Celtic and Germanic" pre-conversion belief systems.

It would really depend on what you mean by Celtic and Germanic, and what period you are imagining. The rich material culture of the La Tène and Hallstatt cultures, which are generally considered Celtic, covered what what generally be thought of as Germanic regions today, named as they are for regions in Switzerland and Austria respectively.

They also spanned several hundred years, and represented a melange of local and regional cultures... Adding to this what is known about Celtic belief systems tends towards the broad-strokes, and is the result of a lot of linguistic reconstruction, archaeology and Classical analysis, so... basically what I'm getting at is you are asking a very challenging question.