Hello from a "quad-wingual" pilot:
In the USHGA, "biwingual" (pronounced like bilingual) means flying
both HG and PG. I fly (mostly) sailplane and also single engine,
besides having (currently under-utilised) ratings in HG and PG. Also a
member of GFA (Gliding Federation of Australia) who's magazine is
shared by HGFA (guess). A great concept, since it's all the same thing.
FYI, here are some statistics from the USHGA website. New ratings for
the last three years in the USHGA are listed below. These could be
add-on ratings. I would like to believe there is that much activity in
soaring, but think not. See earlier postings about unused "collected"
glider ratings.
Jim

2005/12 17
2005/11 94
2005/10 178
2005/9 232
2005/8 252
2005/7 226
2005/6 211
2005/5 214
2005/4 161
2005/3 171
2005/2 92
2005/1 68
2004/12 107
2004/11 136
2004/10 229
2004/9 208
2004/8 312
2004/7 243
2004/6 281
2004/5 260
2004/4 173
2004/3 129
2004/2 89
2004/1 121
2003/12 95
2003/11 107
2003/10 225
2003/9 319
2003/8 300
2003/7 306
2003/6 240
2003/5 273
2003/4 186
2003/3 155
2003/2 126
2003/1 123
2002/12 49