Add pl and cs languages

packages/artplayer/src/i18n/index.js

@@ -1,6 +1,8 @@
 import { mergeDeep } from '../utils';
 import zhCn from './zh-cn.json';
 import zhTw from './zh-tw.json';
+import pl from './pl.json';
+import cs from './cs.json';
 
 export default class I18n {
     constructor(art) {
@@ -8,6 +10,8 @@ export default class I18n {
         this.languages = {
             'zh-cn': zhCn,
             'zh-tw': zhTw,
+            "pl": pl,
+            "cs": cs,
         };
         this.init();
     }