diff --git a/_cache_service_worker.js b/_cache_service_worker.js
index 10fe7bb..c60c891 100644
--- a/_cache_service_worker.js
+++ b/_cache_service_worker.js
@@ -29,7 +29,7 @@ caches.keys().then(function(cacheNames){
 });
 
 var PRECACHE_ID='rom-patcher-js';
-var PRECACHE_VERSION='v11';
+var PRECACHE_VERSION='v12';
 var PRECACHE_URLS=[
 	'/RomPatcher.js/','/RomPatcher.js/index.html',
 	'/RomPatcher.js/manifest.json',
diff --git a/index.html b/index.html
index ee88382..682d058 100644
--- a/index.html
+++ b/index.html
@@ -111,7 +111,7 @@
 		<div class="row" id="row-addheader" style="display:none">
 			<div class="leftcol"></div>
 			<div class="rightcol">
-				<input type="checkbox" id="checkbox-addheader" /> <label for="checkbox-addheader" data-localize="add_header">Add temporary header:</label> <small>(<label id="headersize" for="checkbox-addheader"></label>)</small>
+				<input type="checkbox" id="checkbox-addheader" /> <label for="checkbox-addheader" data-localize="add_header">Add temporary header</label> <small>(<label id="headersize" for="checkbox-addheader"></label>)</small>
 			</div>
 		</div>
 
@@ -166,14 +166,23 @@
 	</div>
 </div>
 
-<div id="snackbar" class="closed"></div>
 
 
 
 
 <!-- FOOTER -->
 <footer>
-	Rom Patcher JS <small>v2.3b</small> by <a href="/">Marc Robledo</a>
+	<div>
+		<select id="select-language" onchange="setLanguage(this.value)">
+			<option value="en">English</option>
+			<option value="de">Deutsch</option>
+			<option value="es">Español</option>
+			<option value="ca">Català</option>
+			<option value="ru">Russian</option>
+		</select>
+	</div>
+
+	Rom Patcher JS <small>v2.4</small> by <a href="/">Marc Robledo</a>
 	<br />
 	<i class="icon github"></i> <a href="https://github.com/marcrobledo/RomPatcher.js/" target="_blank">See on GitHub</a>
 	<i class="icon heart"></i> <a href="https://www.paypal.me/marcrobledo/5" target="_blank" rel="nofollow">Donate</a>
diff --git a/js/RomPatcher.js b/js/RomPatcher.js
index c0cbd1f..e38add2 100644
--- a/js/RomPatcher.js
+++ b/js/RomPatcher.js
@@ -1,4 +1,4 @@
-/* Rom Patcher JS v20200915 - Marc Robledo 2016-2020 - http://www.marcrobledo.com/license */
+/* Rom Patcher JS v20201106 - Marc Robledo 2016-2020 - http://www.marcrobledo.com/license */
 
 const TOO_BIG_ROM_SIZE=67108863;
 const HEADERS_INFO=[
@@ -176,6 +176,23 @@ function _parseROM(){
 }
 
 
+
+function setLanguage(langCode){
+	if(typeof LOCALIZATION[langCode]==='undefined')
+		langCode='en';
+
+	userLanguage=LOCALIZATION[langCode];
+
+	var translatableElements=document.querySelectorAll('*[data-localize]');
+	for(var i=0; i<translatableElements.length; i++){
+		translatableElements[i].innerHTML=_(translatableElements[i].dataset.localize);
+	}
+	
+	if(typeof localStorage!=='undefined'){
+		localStorage.setItem('rompatcher-js-lang', langCode);
+	}
+}
+
 /* initialize app */
 addEvent(window,'load',function(){
 	/* zip-js web worker */
@@ -192,15 +209,11 @@ addEvent(window,'load',function(){
 
 	/* language */
 	var langCode=(navigator.language || navigator.userLanguage).substr(0,2);
-	if(typeof LOCALIZATION[langCode]==='object'){
-		userLanguage=LOCALIZATION[langCode];
-	}else{
-		userLanguage=LOCALIZATION.en;
-	}
-	var translatableElements=document.querySelectorAll('*[data-localize]');
-	for(var i=0; i<translatableElements.length; i++){
-		translatableElements[i].innerHTML=_(translatableElements[i].dataset.localize);
-	}
+	if(typeof localStorage!=='undefined' && localStorage.getItem('rompatcher-js-lang'))
+		langCode=localStorage.getItem('rompatcher-js-lang');
+	el('select-language').value=langCode;
+	setLanguage(langCode);
+
 	
 	el('row-file-patch').title=_('compatible_formats')+' IPS, UPS, APS, BPS, RUP, PPF, MOD (Paper Mario Star Rod), xdelta';
 	
@@ -437,8 +450,21 @@ function preparePatchedRom(originalRom, patchedRom, headerSize){
 		}
 	}
 
+
+
+	/* fix checksum if needed */
+	//var fixedChecksum=fixConsoleChecksum(patchedRom);
+
+
+
+
 	setMessage('apply');
 	patchedRom.save();
+
+
+	/*if(fixedChecksum){
+		setMessage('apply','Checksum was fixed','warning');
+	}*/
 	
 	//debug: create unheadered patch
 	/*if(headerSize && el('checkbox-addheader').checked){
diff --git a/js/crc.js b/js/crc.js
index 785db84..b2d4c9e 100644
--- a/js/crc.js
+++ b/js/crc.js
@@ -1,4 +1,4 @@
-/* Rom Patcher JS - CRC32/MD5/SHA-1 calculators v20181017 - Marc Robledo 2016-2018 - http://www.marcrobledo.com/license */
+/* Rom Patcher JS - CRC32/MD5/SHA-1/checksums calculators v20200926 - Marc Robledo 2016-2020 - http://www.marcrobledo.com/license */
 
 function padZeroes(intVal, nBytes){
 	var hexString=intVal.toString(16);
@@ -102,4 +102,131 @@ function adler32(marcFile, offset, len){
 	}
 
 	return ((b<<16) | a)>>>0;
+}
+
+
+
+
+/* CRC16 */
+/*
+const CRC16_TABLE=(function(){
+	var c,crcTable=[];
+	for(var n=0;n<256;n++){
+		c=n;
+		for(var k=0;k<8;k++)
+			c=((c&1)?(0x8408^(c>>>1)):(c>>>1));
+		crcTable[n]=c;
+	}
+	return crcTable;
+}());
+function crc16(marcFile){
+	var crc=0^(-1);
+
+	for(var i=0;i<marcFile._u8array.length;i++)
+		crc=((crc>>>8)&0x0ff)^CRC16_TABLE[(crc^marcFile._u8array[i])&0xff];
+
+	return ((crc^(-1))>>>0) & 0xffff;
+}
+*/
+
+
+
+		
+		
+		
+
+/* specific ROM checksums */
+/* this is unused code, might be used in a future so ROM checksums can be fixed after patching */
+const CONSOLES=[
+	{
+		title:'Sega Mega Drive/Genesis',
+		MEGADRIVE_LOGO:[0x53, 0x45, 0x47, 0x41, 0x20, 0x4d, 0x45, 0x47, 0x41, 0x20, 0x44, 0x52],
+		GENESIS_LOGO:[0x53, 0x45, 0x47, 0x41, 0x20, 0x47, 0x45, 0x4e, 0x45, 0x53, 0x49, 0x53],
+		checkHeader:function(marcFile){
+			var megadrive=true;
+			var genesis=true;
+			for(var i=0; i<12 && (megadrive || genesis); i++){
+				if(marcFile._u8array[0x100+i]!==this.MEGADRIVE_LOGO[i])
+					megadrive=false;
+				if(marcFile._u8array[0x100+i]!==this.GENESIS_LOGO[i])
+					genesis=false;
+			}
+			return megadrive || genesis;
+		},
+		getChecksum:function(marcFile){
+			return (marcFile._u8array[0x018e]<<8) + marcFile._u8array[0x018f];
+		},
+		recalculateChecksum:function(marcFile){
+			var checksum=0;
+
+			for(var i=0x200; i<marcFile.fileSize; i+=2)
+				checksum=(checksum + (((marcFile._u8array[i]<<8) + marcFile._u8array[i+1])>>>0)) & 0xffff;
+
+			return checksum
+		},
+		updateChecksum:function(marcFile, newChecksum){
+			marcFile._u8array[0x18e]=newChecksum>>8;
+			marcFile._u8array[0x18f]=newChecksum & 0xff;
+		}
+	},{
+		title:'Game Boy',
+		NINTENDO_LOGO:[0xce, 0xed, 0x66, 0x66, 0xcc, 0x0d, 0x00, 0x0b, 0x03, 0x73, 0x00, 0x83, 0x00, 0x0c, 0x00, 0x0d],
+		checkHeader:function(marcFile){
+			for(var i=0; i<this.NINTENDO_LOGO.length; i++){
+				if(marcFile._u8array[0x104+i]!==this.NINTENDO_LOGO[i])
+					return false;
+			}
+			return true;
+		},
+		getChecksum:function(marcFile){
+			return marcFile._u8array[0x14d]
+		},
+		recalculateChecksum:function(marcFile){
+			var checksum=0;
+
+			for(var i=0x134; i<0x014d; i++){
+				checksum=(checksum - marcFile._u8array[i] - 1) & 0xff;
+			}
+
+			return checksum
+		},
+		updateChecksum:function(marcFile, newChecksum){
+			marcFile._u8array[0x014d]=newChecksum;
+
+
+			/* global checksum isn't checked by real hw, but fix it anyway */
+			var globalChecksumOld=(marcFile._u8array[0x014e]<<8) + marcFile._u8array[0x014f];
+			var globalChecksumNew=0;
+			for(var i=0x0000; i<0x014e; i++)
+				globalChecksumNew=((globalChecksumNew + marcFile._u8array[i]) >>> 0) & 0xffff;
+			for(i=0x0150;i<marcFile.fileSize; i++)
+				globalChecksumNew=((globalChecksumNew + marcFile._u8array[i]) >>> 0) & 0xffff;
+			if(globalChecksumOld!==globalChecksumNew){
+				marcFile._u8array[0x014e]=globalChecksumNew>>8;
+				marcFile._u8array[0x014f]=globalChecksumNew & 0xff;
+			}
+		}
+	}
+];
+function checkConsole(marcFile){
+	return false;
+}
+function fixConsoleChecksum(marcFile){
+	var system=false;
+	for(var i=0; i<CONSOLES.length && !system; i++)
+		if(CONSOLES[i].checkHeader(marcFile))
+			system=CONSOLES[i];
+	if(!system)
+		return false;
+	
+	var oldChecksum=console.getChecksum(marcFile);
+	var newChecksum=console.recalculateChecksum(marcFile);
+	
+	if(oldChecksum!==newChecksum)
+		if(alert('Fix '+console.title+' checksum?')){
+			console.updateChecksum(marcFile, newChecksum);
+			return true;
+		}
+	
+	return false;
 }
\ No newline at end of file
diff --git a/style/RomPatcher.css b/style/RomPatcher.css
index ca4ffe5..69f70e0 100644
--- a/style/RomPatcher.css
+++ b/style/RomPatcher.css
@@ -1,9 +1,9 @@
-/* WebApps CSS template by Marc Robledo v20190531 */
+/* WebApps CSS template by Marc Robledo v20191106 */
 /* minify at https://cssminifier.com/ + https://www.base64-image.de/ */
 
 /* @FONT-FACES */
 @import url('https://fonts.googleapis.com/css?family=Open+Sans:400,700');
-@import url(https://fonts.googleapis.com/css?family=Roboto+Mono:300);
+@import url('https://fonts.googleapis.com/css?family=Roboto+Mono:300');
 
 body{
 	margin:0;
@@ -52,7 +52,6 @@ footer{padding: 50px 0 20px}
 
 
 /* icons */
-
 footer .icon, #crc32.valid:after{
 	background-image: url('data:image/png;base64,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');
 }
@@ -180,7 +179,16 @@ select::-ms-expand{display:none}
 input[type=file].enabled:hover,select.enabled:hover{background-color:#dee1e1}
 input[type=file].disabled,select.disabled{background-color:transparent}
 
-
+#select-language{
+	background-color:transparent;
+	color:white;
+	cursor:pointer;
+	background-image:url("data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHN0eWxlPSJmaWxsOiNmZmYiIHZlcnNpb249IjEuMSIgeD0iMTJweCIgeT0iMHB4IiB3aWR0aD0iMjRweCIgaGVpZ2h0PSIzcHgiIHZpZXdCb3g9IjAgMCA2IDMiIGVuYWJsZS1iYWNrZ3JvdW5kPSJuZXcgMCAwIDYgMyIgeG1sOnNwYWNlPSJwcmVzZXJ2ZSI+PHBvbHlnb24gcG9pbnRzPSI1Ljk5MiwwIDIuOTkyLDMgLTAuMDA4LDAgIi8+PC9zdmc+");
+}
+#select-language:hover{
+	background-color:#2b2e33;
+	cursor:pointer;
+}
 
 
 
@@ -210,7 +218,7 @@ button.enabled:active{
 	transform:translateY(1px)
 }
 button:disabled{opacity:.35 !important;cursor:not-allowed}
-button.close{color:white;background-color:#}
+
 button.no-text.with-icon:before{margin-right:0px}