History.back in JS

I will make a function, where I need information on the previous web page. Is there a document.location function where I can get this information? If the previous page is uk.htm then the language variable is "english". I have tried the code below, but it doesn't work? I only need information on which site was previous, I don't want to go back to this page.

Code:

---

function validate_website() {
if (history.back() == "uk.htm") {
  language_var == "english"
  }
}
if (history.back() == "d.htm") {
  language_var == "german"
  }
}
}

---

try this

if (history.previous.indexOf("uk.htm") != -1) { language_var = "english"}

and if you want ot assign value to var use = not ==
== is to compare