Fix variable lang in language.js

src/js/language.js

@@ -23,7 +23,7 @@ window.addEventListener('load', function() {
 // add listener to languageOptions for collecting data in localStorage
 Array.from(languageOptions).map((option) => {
 	option.addEventListener('click', function() {
-		lang = option.dataset['lang'];
+		let lang = option.dataset['lang'];
 		localStorage.language = lang;
 	})
 })