Feat: more preferences (#106)

* add ffmpeg command check

* may switch language

* tweak

enjoy/src/types/enjoy-app.d.ts

@@ -76,6 +76,8 @@ type EnjoyAppType = {
     ) => Promise<void>;
     getFfmpegConfig: () => Promise<FfmpegConfigType>;
     setFfmpegConfig: () => Promise<void>;
+    getLanguage: () => Promise<string>;
+    switchLanguage: (language: string) => Promise<void>;
   };
   fs: {
     ensureDir: (path: string) => Promise<boolean>;
@@ -177,6 +179,7 @@ type EnjoyAppType = {
   };
   ffmpeg: {
     download: () => Promise<FfmpegConfigType>;
+    check: () => Promise<boolean>;
   };
   download: {
     onState: (callback: (event, state) => void) => void;