Add eslint rule and fix as many issues as possible

frontend/src/i18n.ts

@@ -1,7 +1,7 @@
-import { initReactI18next } from 'react-i18next';
-import i18n from 'i18next';
-import LanguageDetector from 'i18next-browser-languagedetector';
-import Backend from 'i18next-http-backend';
+import { initReactI18next } from "react-i18next";
+import i18n from "i18next";
+import LanguageDetector from "i18next-browser-languagedetector";
+import Backend from "i18next-http-backend";
 // don't want to use this?
 // have a look at the Quick start guide
 // for passing in lng and translations on init
@@ -19,13 +19,13 @@ i18n
   // init i18next
   // for all options read: https://www.i18next.com/overview/configuration-options
   .init({
-    fallbackLng: 'en',
-    supportedLngs: ['en', 'ko', 'fr', 'pt-BR', 'pt-PT', 'es'],
-    debug: process.env.NODE_ENV === 'development',
+    fallbackLng: "en",
+    supportedLngs: ["en", "ko", "fr", "pt-BR", "pt-PT", "es"],
+    debug: process.env.NODE_ENV === "development",
     detection: {
-      lookupLocalStorage: 'lang'
+      lookupLocalStorage: "lang"
     },
-    ns: ['translations'],
+    ns: ["translations"],
     interpolation: {
       escapeValue: false // not needed for react as it escapes by default
     },