text <- c("       Hi,  this is a   	good  	time to   	start working   	together.",
"Hi,  this is a   good  time to   start working   together.",
"Hi,  this is a   good  time to   start working   together.                         ")
gsub("(\\S)\\s{2,}(?=\\S)", "\\1 ", text, perl=TRUE)
stringr::str_replace_all(text, "(\\S)\\s{2,}(?=\\S)", "\\1 ")
## Or, if the whitespace to leep is  the last whitespace in those matched
gsub("(\\S)(\\s){2,}(?=\\S)", "\\1\\2", text, perl=TRUE)
stringr::str_replace_all(text, "(\\S)(\\s){2,}(?=\\S)", "\\1\\2")