feat(i18n): Add translation fields for de, en, ja, km, zhcn

- Update translation index to support Korean
  `application/src/translation/index.ts`
- Update translation indexes
  `application/src/translation/{de,en,ja,km,zhcn}/index.ts`
- Update dropdown menu item in dashboard header
  `application/src/components/dashboard/Header.tsx`

application/src/components/dashboard/Header.tsx

@@ -116,6 +116,9 @@ export const Header = ({
             <DropdownMenuItem onClick={() => setLanguage("de")} className={language === "de" ? "bg-accent" : ""}>
               {t("Deutsch")}
             </DropdownMenuItem>
+            <DropdownMenuItem onClick={() => setLanguage("ko")} className={language === "ko" ? "bg-accent" : ""}>
+              {t("korean")}
+            </DropdownMenuItem>
             <DropdownMenuItem onClick={() => setLanguage("ja")} className={language === "ja" ? "bg-accent" : ""}>
               {t("japanese")}
             </DropdownMenuItem>