BC series follow CBE, while 2N -many of them EBCYou might try "ECA" for transistor comparison books.
E.g. looking up 2N222 you'll find the equivalent "BC" type, here BC547.
2Nxxx and BCxxx are slightly different in collector current and, as already mentioned by audioguru, they are sometimes different in pin layout.
BC-transistors are all E-B-C, 2N types might be B-E-C.
2N3904 (NPN) can be substituted by BC547, 2N3906 (PNP) by BC557.
I you don't need comparison tables very often you might get the info online at ECA - Semiconductor Information Resource Since 1970
Online information is charged with a small fee.
BTW, buying 2N transistors in Germany they are not called "American transistors" but "Japanese transistors".