OK, that seems right. I dont understand exactly what kind of R datatype rbind is giving us, but it does work. your second solution is probably easiest though this seems to give the same result:

filters = list(
  c("Country/CountryName", "EQUAL", "USA"),
  c("Gender/GenderName", "EQUAL", "m")
)
filters = append(filters, list(c("Language/LanguageId", "EQUAL", "French")))

labkey.data2 <- labkey.selectRows(
  baseUrl="https://www.labkey.org",
  folderPath="/home/Demos/Study/demo",
  schemaName="study",
  queryName="Demographics",
  colFilter=do.call(makeFilter, filters)
)
print(nrow(labkey.data2))

thanks for the help.