diff --git a/data/web/inc/vars.inc.php b/data/web/inc/vars.inc.php
index 177c7dd9..15077801 100644
--- a/data/web/inc/vars.inc.php
+++ b/data/web/inc/vars.inc.php
@@ -80,27 +80,28 @@ $DEFAULT_LANG = 'en';
 
 // Available languages
 // https://www.iso.org/obp/ui/#search
-// https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes
+// https://en.wikipedia.org/wiki/IETF_language_tag
 $AVAILABLE_LANGUAGES = array(
-  'cs' => 'Čeština (Czech)',
-  'da' => 'Danish (Dansk)',
-  'de' => 'Deutsch (German)',
-  'en' => 'English',
-  'es' => 'Español (Spanish)',
-  'fi' => 'Suomi (Finish)',
-  'fr' => 'Français (French)',
-  'hu' => 'Magyar (Hungarian)',
-  'it' => 'Italiano (Italian)',
-  'ko' => '한국어 (Korean)',
-  'lv' => 'latviešu (Latvian)',
-  'nl' => 'Nederlands (Dutch)',
-  'pl' => 'Język Polski (Polish)',
-  'pt' => 'Português (Portuguese)',
-  'ro' => 'Română (Romanian)',
-  'ru' => 'Pусский (Russian)',
-  'sk' => 'Slovenčina (Slovak)',
-  'sv' => 'Svenska (Swedish)',
-  'uk' => 'Українська (Ukrainian)',
+  // 'ca-es' => 'Català (Catalan)',
+  'cs-cz' => 'Čeština (Czech)',
+  'da-dk' => 'Danish (Dansk)',
+  'de-de' => 'Deutsch (German)',
+  'en-gb' => 'English',
+  'es-es' => 'Español (Spanish)',
+  'fi-fi' => 'Suomi (Finish)',
+  'fr-fr' => 'Français (French)',
+  'hu-hu' => 'Magyar (Hungarian)',
+  'it-it' => 'Italiano (Italian)',
+  'ko-kr' => '한국어 (Korean)',
+  'lv-lv' => 'latviešu (Latvian)',
+  'nl-nl' => 'Nederlands (Dutch)',
+  'pl-pl' => 'Język Polski (Polish)',
+  'pt-pt' => 'Português (Portuguese)',
+  'ro-ro' => 'Română (Romanian)',
+  'ru-ru' => 'Pусский (Russian)',
+  'sk-sk' => 'Slovenčina (Slovak)',
+  'sv-se' => 'Svenska (Swedish)',
+  'uk-ua' => 'Українська (Ukrainian)',
   'zh-cn' => '简体中文 (Simplified Chinese)',
   'zh-tw' => '繁體中文 (Traditional Chinese)',
 );
diff --git a/data/web/lang/lang.ca.json b/data/web/lang/lang.ca-es.json
similarity index 100%
rename from data/web/lang/lang.ca.json
rename to data/web/lang/lang.ca-es.json
diff --git a/data/web/lang/lang.cs.json b/data/web/lang/lang.cs-cz.json
similarity index 100%
rename from data/web/lang/lang.cs.json
rename to data/web/lang/lang.cs-cz.json
diff --git a/data/web/lang/lang.da.json b/data/web/lang/lang.da-dk.json
similarity index 100%
rename from data/web/lang/lang.da.json
rename to data/web/lang/lang.da-dk.json
diff --git a/data/web/lang/lang.de.json b/data/web/lang/lang.de-de.json
similarity index 100%
rename from data/web/lang/lang.de.json
rename to data/web/lang/lang.de-de.json
diff --git a/data/web/lang/lang.en.json b/data/web/lang/lang.en-gb.json
similarity index 100%
rename from data/web/lang/lang.en.json
rename to data/web/lang/lang.en-gb.json
diff --git a/data/web/lang/lang.es.json b/data/web/lang/lang.es-es.json
similarity index 100%
rename from data/web/lang/lang.es.json
rename to data/web/lang/lang.es-es.json
diff --git a/data/web/lang/lang.fi.json b/data/web/lang/lang.fi-fi.json
similarity index 100%
rename from data/web/lang/lang.fi.json
rename to data/web/lang/lang.fi-fi.json
diff --git a/data/web/lang/lang.fr.json b/data/web/lang/lang.fr-fr.json
similarity index 100%
rename from data/web/lang/lang.fr.json
rename to data/web/lang/lang.fr-fr.json
diff --git a/data/web/lang/lang.hu.json b/data/web/lang/lang.hu-hu.json
similarity index 100%
rename from data/web/lang/lang.hu.json
rename to data/web/lang/lang.hu-hu.json
diff --git a/data/web/lang/lang.it.json b/data/web/lang/lang.it-it.json
similarity index 100%
rename from data/web/lang/lang.it.json
rename to data/web/lang/lang.it-it.json
diff --git a/data/web/lang/lang.ko.json b/data/web/lang/lang.ko-kr.json
similarity index 100%
rename from data/web/lang/lang.ko.json
rename to data/web/lang/lang.ko-kr.json
diff --git a/data/web/lang/lang.lv.json b/data/web/lang/lang.lv-lv.json
similarity index 100%
rename from data/web/lang/lang.lv.json
rename to data/web/lang/lang.lv-lv.json
diff --git a/data/web/lang/lang.nl.json b/data/web/lang/lang.nl-nl.json
similarity index 100%
rename from data/web/lang/lang.nl.json
rename to data/web/lang/lang.nl-nl.json
diff --git a/data/web/lang/lang.pl.json b/data/web/lang/lang.pl-pl.json
similarity index 100%
rename from data/web/lang/lang.pl.json
rename to data/web/lang/lang.pl-pl.json
diff --git a/data/web/lang/lang.pt.json b/data/web/lang/lang.pt-pt.json
similarity index 100%
rename from data/web/lang/lang.pt.json
rename to data/web/lang/lang.pt-pt.json
diff --git a/data/web/lang/lang.ro.json b/data/web/lang/lang.ro-ro.json
similarity index 100%
rename from data/web/lang/lang.ro.json
rename to data/web/lang/lang.ro-ro.json
diff --git a/data/web/lang/lang.ru.json b/data/web/lang/lang.ru-ru.json
similarity index 100%
rename from data/web/lang/lang.ru.json
rename to data/web/lang/lang.ru-ru.json
diff --git a/data/web/lang/lang.sk.json b/data/web/lang/lang.sk-sk.json
similarity index 100%
rename from data/web/lang/lang.sk.json
rename to data/web/lang/lang.sk-sk.json
diff --git a/data/web/lang/lang.sv.json b/data/web/lang/lang.sv-se.json
similarity index 100%
rename from data/web/lang/lang.sv.json
rename to data/web/lang/lang.sv-se.json
diff --git a/data/web/lang/lang.uk.json b/data/web/lang/lang.uk-ua.json
similarity index 100%
rename from data/web/lang/lang.uk.json
rename to data/web/lang/lang.uk-ua.json