diff --git a/sonoff/_releasenotes.ino b/sonoff/_releasenotes.ino
index 721b8d376..1ad9bb410 100644
--- a/sonoff/_releasenotes.ino
+++ b/sonoff/_releasenotes.ino
@@ -1,5 +1,6 @@
 /* 5.12.0e
  * Add a second TLS fingerprint to allow switching keys in TLS mode (#2033, #2102)
+ * Add HTML language header in local language (#2123)
  *
  * 5.12.0d
  * Add support for optional MQTT drivers to be selected in user_config.h (#1992)
diff --git a/sonoff/language/cz-CZ.h b/sonoff/language/cs-CZ.h
similarity index 98%
rename from sonoff/language/cz-CZ.h
rename to sonoff/language/cs-CZ.h
index f017e9de5..c799d9a37 100644
--- a/sonoff/language/cz-CZ.h
+++ b/sonoff/language/cs-CZ.h
@@ -1,5 +1,5 @@
 /*
-  cz-CZ.h - localization for Czech with fonetick - Czech for Sonoff-Tasmota
+  cz-CZ.h - localization for Czech with diacritics - Czech for Sonoff-Tasmota
 
   Copyright (C) 2018  Theo Arends (translated by vs)
 
@@ -17,8 +17,8 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#ifndef _LANGUAGE_CZ_CZ_H_
-#define _LANGUAGE_CZ_CZ_H_
+#ifndef _LANGUAGE_CS_CZ_H_
+#define _LANGUAGE_CS_CZ_H_
 
 /*************************** ATTENTION *******************************\
  *
@@ -32,6 +32,9 @@
 
 //#define LANGUAGE_MODULE_NAME         // Enable to display "Module Generic" (ie Spanish), Disable to display "Generic Module" (ie English)
 
+// HTML (ISO 639-1) Language Code
+#define D_HTML_LANGUAGE "cs"
+
 // "2017-03-07T11:08:02" - ISO8601:2004
 #define D_YEAR_MONTH_SEPARATOR "-"
 #define D_MONTH_DAY_SEPARATOR "-"
@@ -455,4 +458,4 @@
 #define D_LOG_UPNP "UPP: "         // UPnP
 #define D_LOG_WIFI "WIF: "         // Wifi
 
-#endif  // _LANGUAGE_CZ_CZ_H_
+#endif  // _LANGUAGE_CS_CZ_H_
diff --git a/sonoff/language/de-DE.h b/sonoff/language/de-DE.h
index d43055b67..14c525a75 100644
--- a/sonoff/language/de-DE.h
+++ b/sonoff/language/de-DE.h
@@ -32,6 +32,9 @@
 
 //#define LANGUAGE_MODULE_NAME         // Enable to display "Module Generic" (ie Spanish), Disable to display "Generic Module" (ie English)
 
+// HTML (ISO 639-1) Language Code
+#define D_HTML_LANGUAGE "de"
+
 // "2017-03-07T11:08:02" - ISO8601:2004
 #define D_YEAR_MONTH_SEPARATOR "."
 #define D_MONTH_DAY_SEPARATOR "."
diff --git a/sonoff/language/en-GB.h b/sonoff/language/en-GB.h
index 905ed5d9b..80c8518df 100644
--- a/sonoff/language/en-GB.h
+++ b/sonoff/language/en-GB.h
@@ -32,6 +32,9 @@
 
 //#define LANGUAGE_MODULE_NAME         // Enable to display "Module Generic" (ie Spanish), Disable to display "Generic Module" (ie English)
 
+// HTML (ISO 639-1) Language Code
+#define D_HTML_LANGUAGE "en"
+
 // "2017-03-07T11:08:02" - ISO8601:2004
 #define D_YEAR_MONTH_SEPARATOR "-"
 #define D_MONTH_DAY_SEPARATOR "-"
diff --git a/sonoff/language/es-AR.h b/sonoff/language/es-AR.h
index c46bfa1d5..fee5c40ea 100644
--- a/sonoff/language/es-AR.h
+++ b/sonoff/language/es-AR.h
@@ -32,6 +32,9 @@
 
 #define LANGUAGE_MODULE_NAME         // Enable to display "Module Generic" (ie Spanish), Disable to display "Generic Module" (ie English)
 
+// HTML (ISO 639-1) Language Code
+#define D_HTML_LANGUAGE "es"
+
 // "2017-03-07T11:08:02" - ISO8601:2004
 #define D_YEAR_MONTH_SEPARATOR "-"
 #define D_MONTH_DAY_SEPARATOR "-"
diff --git a/sonoff/language/fr-FR.h b/sonoff/language/fr-FR.h
index 653887508..8ec6cd1f7 100644
--- a/sonoff/language/fr-FR.h
+++ b/sonoff/language/fr-FR.h
@@ -32,6 +32,9 @@
 
 #define LANGUAGE_MODULE_NAME         // Enable to display "Module Generic" (ie Spanish), Disable to display "Generic Module" (ie English)
 
+// HTML (ISO 639-1) Language Code
+#define D_HTML_LANGUAGE "fr"
+
 // "2017-03-07T11:08:02" - ISO8601:2004
 #define D_YEAR_MONTH_SEPARATOR "-"
 #define D_MONTH_DAY_SEPARATOR "-"
diff --git a/sonoff/language/hu-HU.h b/sonoff/language/hu-HU.h
index 9ce316cf9..c07024f11 100644
--- a/sonoff/language/hu-HU.h
+++ b/sonoff/language/hu-HU.h
@@ -32,6 +32,9 @@
 
 //#define LANGUAGE_MODULE_NAME         // Enable to display "Module Generic" (ie Spanish), Disable to display "Generic Module" (ie English)
 
+// HTML (ISO 639-1) Language Code
+#define D_HTML_LANGUAGE "hu"
+
 // "2017-03-07T11:08:02" - ISO8601:2004
 #define D_YEAR_MONTH_SEPARATOR "."
 #define D_MONTH_DAY_SEPARATOR "."
diff --git a/sonoff/language/it-IT.h b/sonoff/language/it-IT.h
index 0e0f4594f..07499c821 100644
--- a/sonoff/language/it-IT.h
+++ b/sonoff/language/it-IT.h
@@ -32,6 +32,9 @@
 
 #define LANGUAGE_MODULE_NAME         // Enable to display "Module Generic" (ie Spanish), Disable to display "Generic Module" (ie English)
 
+// HTML (ISO 639-1) Language Code
+#define D_HTML_LANGUAGE "it"
+
 // "2017-03-07T11:08:02" - ISO8601:2004
 #define D_YEAR_MONTH_SEPARATOR "-"
 #define D_MONTH_DAY_SEPARATOR "-"
diff --git a/sonoff/language/nl-NL.h b/sonoff/language/nl-NL.h
index 0932a7326..918f9bddd 100644
--- a/sonoff/language/nl-NL.h
+++ b/sonoff/language/nl-NL.h
@@ -32,6 +32,9 @@
 
 //#define LANGUAGE_MODULE_NAME         // Enable to display "Module Generic" (ie Spanish), Disable to display "Generic Module" (ie English)
 
+// HTML (ISO 639-1) Language Code
+#define D_HTML_LANGUAGE "nl"
+
 // "2017-03-07T11:08:02" - ISO8601:2004
 #define D_YEAR_MONTH_SEPARATOR "-"
 #define D_MONTH_DAY_SEPARATOR "-"
diff --git a/sonoff/language/pl-PL.h b/sonoff/language/pl-PL.h
index 1b2bbb099..4542d826d 100644
--- a/sonoff/language/pl-PL.h
+++ b/sonoff/language/pl-PL.h
@@ -32,6 +32,9 @@
 
 //#define LANGUAGE_MODULE_NAME         // Enable to display "Module Generic" (ie Spanish), Disable to display "Generic Module" (ie English)
 
+// HTML (ISO 639-1) Language Code
+#define D_HTML_LANGUAGE "pl"
+
 // "2017-03-07T11:08:02" - ISO8601:2004
 #define D_YEAR_MONTH_SEPARATOR "-"
 #define D_MONTH_DAY_SEPARATOR "-"
diff --git a/sonoff/language/pt-PT.h b/sonoff/language/pt-PT.h
index cc3b74a04..db42667f5 100644
--- a/sonoff/language/pt-PT.h
+++ b/sonoff/language/pt-PT.h
@@ -32,6 +32,9 @@
 
 //#define LANGUAGE_MODULE_NAME         // Enable to display "Module Generic" (ie Spanish), Disable to display "Generic Module" (ie English)
 
+// HTML (ISO 639-1) Language Code
+#define D_HTML_LANGUAGE "pt"
+
 // "2017-03-07T11:08:02" - ISO8601:2004
 #define D_YEAR_MONTH_SEPARATOR "-"
 #define D_MONTH_DAY_SEPARATOR "-"
diff --git a/sonoff/language/ru-RU.h b/sonoff/language/ru-RU.h
index d5483b504..1b60f0e4a 100644
--- a/sonoff/language/ru-RU.h
+++ b/sonoff/language/ru-RU.h
@@ -32,6 +32,9 @@
 
 //#define LANGUAGE_MODULE_NAME         // Enable to display "Module Generic" (ie Spanish), Disable to display "Generic Module" (ie English)
 
+// HTML (ISO 639-1) Language Code
+#define D_HTML_LANGUAGE "ru"
+
 // "2017-03-07T11:08:02" - ISO8601:2004
 #define D_YEAR_MONTH_SEPARATOR "-"
 #define D_MONTH_DAY_SEPARATOR "-"
diff --git a/sonoff/language/zh-CN.h b/sonoff/language/zh-CN.h
index feff61a23..d52e648f9 100644
--- a/sonoff/language/zh-CN.h
+++ b/sonoff/language/zh-CN.h
@@ -32,6 +32,9 @@
 
 //#define LANGUAGE_MODULE_NAME         // Enable to display "Module Generic" (ie Spanish), Disable to display "Generic Module" (ie English)
 
+// HTML (ISO 639-1) Language Code
+#define D_HTML_LANGUAGE "zh"
+
 // "2017-03-07T11:08:02" - ISO8601:2004
 #define D_YEAR_MONTH_SEPARATOR "-"
 #define D_MONTH_DAY_SEPARATOR "-"
diff --git a/sonoff/language/zh-TW.h b/sonoff/language/zh-TW.h
index 8ae1618c6..e011dfe3c 100644
--- a/sonoff/language/zh-TW.h
+++ b/sonoff/language/zh-TW.h
@@ -32,6 +32,9 @@
 
 //#define LANGUAGE_MODULE_NAME         // Enable to display "Module Generic" (ie Spanish), Disable to display "Generic Module" (ie English)
 
+// HTML (ISO 639-1) Language Code
+#define D_HTML_LANGUAGE "zh"
+
 // "2017-03-07T11:08:02" - ISO8601:2004
 #define D_YEAR_MONTH_SEPARATOR "-"
 #define D_MONTH_DAY_SEPARATOR "-"
diff --git a/sonoff/user_config.h b/sonoff/user_config.h
index a59d451fd..92a8c160f 100644
--- a/sonoff/user_config.h
+++ b/sonoff/user_config.h
@@ -29,7 +29,7 @@
 \*********************************************************************************************/
 
 // -- Localization --------------------------------
-//#define MY_LANGUAGE            cz-CZ           // Czech without fonetick in Czech
+//#define MY_LANGUAGE            cs-CZ           // Czech in Czech
 //#define MY_LANGUAGE            de-DE           // German in Germany
 //#define MY_LANGUAGE            en-GB           // English in Great Britain. Enabled by Default
 //#define MY_LANGUAGE            es-AR           // Spanish in Argentina
diff --git a/sonoff/webserver.ino b/sonoff/webserver.ino
index fb248a2a7..cc843748f 100644
--- a/sonoff/webserver.ino
+++ b/sonoff/webserver.ino
@@ -29,7 +29,7 @@
 #define STR(x) STR_HELPER(x)
 
 const char HTTP_HEAD[] PROGMEM =
-  "<!DOCTYPE html><html lang=\"en\" class=\"\">"
+  "<!DOCTYPE html><html lang=\"" D_HTML_LANGUAGE "\" class=\"\">"
   "<head>"
   "<meta charset='utf-8'>"
   "<meta name=\"viewport\" content=\"width=device-width,initial-scale=1,user-scalable=no\"/>"