Add Czech locale

frontend/src/stores/language.ts

@@ -18,6 +18,7 @@ const defaultLanguageState = {
     { value: "ja_JP", name: "日本語 (日本)" },
     { value: "it_IT", name: "Italiano" },
     { value: "pl_PL", name: "Polski" },
+    { value: "cs_CZ", name: "Česky" },
   ].sort((a, b) => a.name.localeCompare(b.name)),
 };