R - Convert list to xml in R

I would like to use a website from R. The website is http://soundoftext.com/ where I can download WAV. files with audios from a given text and a language (voice).

There are two steps to download the voice in WAV: 1) Insert text and Select language. And Submit 2) On the new window, click Save and select folder.

Until now, I could get the xml tree, convert it to list and modify the values of text and language. However, I don't know how to convert the list to XML (with the new values) and execute it. Then, I would need to do the second step too.

Here is my code so far:

require(RCurl)
require(XML)
webpage <- getURL("http://soundoftext.com/")
webpage <- readLines(tc <- textConnection(webpage)); close(tc)
pagetree <- htmlTreeParse(webpage, error=function(...){}, useInternalNodes = TRUE)
x<-xmlToList(pagetree)
# Inserting word
x$body$div$div$div$form$div$label$.attrs[[1]]<-"Raúl"
x$body$div$div$div$form$div$label$.attrs[[1]]

# Select language
x$body$div$div$div$form$div$select$option$.attrs<-"es"
x$body$div$div$div$form$div$select$option$.attrs 

I have follow this approach but there is an error with "tag".

Thanks