I believe the timpani needs the appendix "C.G." because that is the required tuning it needs for the piece. One drum is tuned to C and the other to G. But perhaps I'm wrong.
If there are any orchestra or percussion avidists out there let us know.
Your translation is correct, they are Italian names.
The timpani requires the appendix in order to indicate both how many drums are required, and to which pitches they are tuned.
The present urtext-du-jour of the Beethoven 5 (edited by Jonathan del Mar, Barenreiter) has "clarini in do" instead of "trumpet" or "tromba." This is important in that it refers to valveless "natural" trumpets. These sound quite different from modern valved trumpets playing the same pitches, especially if the modern trumpets are not themselves in C.