library(rvest)
library(plyr)
library(dplyr)
options(stringsAsFactors=FALSE)

langUrl <- "http://rosettacode.org/mw/api.php?format=xml&action=query&generator=categorymembers&gcmtitle=Category:Programming%20Languages&prop=categoryinfo&gcmlimit=5000"
langs <- html(langUrl) %>%
  html_nodes('page')

ff <- function(xml_node) {
  language <- xml_node %>% html_attr("title")
  language <- sub("^Category:", "", language)
  npages <- xml_node %>% html_nodes('categoryinfo') %>%
    html_attr("pages")
  c(language, npages)
}
tbl <- ldply(sapply(langs, ff), rbind)
names(tbl) <- c("language", "n")
tbl %>%
  mutate(n=as.integer(n)) %>% 
  arrange(desc(n)) %>%
  head