diff --git a/README b/README
index aca998f..a82b9a3 100644
--- a/README
+++ b/README
@@ -26,14 +26,15 @@ Yo also need to install go dependences:
 # go get gopkg.in/mgo.v2 gopkg.in/mgo.v2/bson github.com/gorilla/sessions \
          github.com/gorilla/securecookie github.com/gorilla/mux \
          github.com/nfnt/resize github.com/cihub/seelog \
-         code.google.com/p/go.crypto/scrypt
+         code.google.com/p/go.crypto/scrypt \
+         github.com/rainycape/cld2
 
 == Installation ==
 === For admins ("for developers" below) ===
 
 Now you can install Trantor itself:
 
-# go get git.gitorious.org/trantor/trantor.git
+# go get -tags prod git.gitorious.org/trantor/trantor.git
 
 You can run trantor in /srv/www/trantor i.e. For this:
 
@@ -63,7 +64,8 @@ $ cd yournames-trantor
 You can edit config.go if you want to change the port and other configuration, by default is 8080
 
 Now you can compile Trantor:
-$ go build
+$ go build -tags prod
+(remove '-tags prod' for a faster compilation without language guessing)
 
 Now you can run it:
 $ ./yourname-trantor
diff --git a/language.go b/language.go
new file mode 100644
index 0000000..8ecc155
--- /dev/null
+++ b/language.go
@@ -0,0 +1,68 @@
+// +build prod
+
+package main
+
+import (
+	"io/ioutil"
+	"strings"
+
+	"git.gitorious.org/go-pkg/epubgo.git"
+	"github.com/rainycape/cld2"
+)
+
+func GuessLang(epub *epubgo.Epub, orig_langs []string) []string {
+	spine, err := epub.Spine()
+	if err != nil {
+		return orig_langs
+	}
+
+	var err_spine error
+	err_spine = nil
+	langs := []string{}
+	for err_spine == nil {
+		html, err := spine.Open()
+		err_spine = spine.Next()
+		if err != nil {
+			continue
+		}
+		defer html.Close()
+
+		buff, err := ioutil.ReadAll(html)
+		if err != nil {
+			continue
+		}
+		langs = append(langs, cld2.Detect(string(buff)))
+	}
+
+	lang := commonLang(langs)
+	if lang != "un" && differentLang(lang, orig_langs) {
+		return []string{lang}
+	}
+	return orig_langs
+}
+
+func commonLang(langs []string) string {
+	count := map[string]int{}
+	for _, l := range langs {
+		count[l]++
+	}
+
+	lang := "un"
+	maxcount := 0
+	for l, c := range count {
+		if c > maxcount && l != "un" {
+			lang = l
+			maxcount = c
+		}
+	}
+	return lang
+}
+
+func differentLang(lang string, orig_langs []string) bool {
+	orig_lang := "un"
+	if len(orig_langs) > 0 && len(orig_langs) >= 2 {
+		orig_lang = strings.ToLower(orig_langs[0][0:2])
+	}
+
+	return orig_lang != lang
+}
diff --git a/language_develop.go b/language_develop.go
new file mode 100644
index 0000000..69ee859
--- /dev/null
+++ b/language_develop.go
@@ -0,0 +1,16 @@
+// +build !prod
+
+// This is a dummy implementation of GuessLang used to make the compilation faster on development
+//
+// To build trantor with the proper language guessing do:
+//   $ go build -tags prod
+
+package main
+
+import (
+	"git.gitorious.org/go-pkg/epubgo.git"
+)
+
+func GuessLang(epub *epubgo.Epub, orig_langs []string) []string {
+	return orig_langs
+}
diff --git a/upload.go b/upload.go
index 743283f..9a61d30 100644
--- a/upload.go
+++ b/upload.go
@@ -124,7 +124,7 @@ func parseFile(epub *epubgo.Epub, store *storage.Store) (metadata map[string]int
 		case "date":
 			book[m] = parseDate(data)
 		case "language":
-			book["lang"] = data
+			book["lang"] = GuessLang(epub, data)
 		case "title", "contributor", "publisher":
 			book[m] = cleanStr(strings.Join(data, ", "))
 		case "identifier":
@@ -140,7 +140,7 @@ func parseFile(epub *epubgo.Epub, store *storage.Store) (metadata map[string]int
 	}
 
 	id = genId()
-	book["id"] = id //TODO
+	book["id"] = id
 	book["cover"] = GetCover(epub, id, store)
 	return book, id
 }