So here we go, hacked together a quick plugin and packaged it for Windows 
If you are using Windows you can download the plugin at https://keybase.pub/phwolfer/picard-plugins/opencc-windows.zip . Extract the ZIP file and place the opencc folder in your Picard plugins folder. You can find the plugin folder by opening Options > Plugins and clicking on âOpen plugin folderâ.
NOTE: Installing this plugin as ZIP file wonât work, you have to extract it. Otherwise the included opencc.dll wonât get found.
UPDATE: Fixed it, things got easier. Download the ZIP file from https://keybase.pub/phwolfer/picard-plugins/opencc.zip , then open Picard Options > Plugins, click on âInstall pluginâŚâ and select the downloaded opencc.zip. This should install and activate the plugin âChinese script conversionâ.
Start (or restart) Picard. The plugin should now show up in Options > Plugins. Activate it. Once activated you can right click on any albums, tracks or files and choose Plugins -> Convert to ⌠Chinese.
Let me know if this plugin works for you. If something in the conversion doesnât work as expected it can probably be changed. OpenCC provides various configurations for the conversion, including conversion to and from Hong Kong and Taiwan variants of the traditional script. For now I have used what is labeled simply âTraditional Chinese to Simplified Chineseâ and âSimplified Chinese to Traditional Chineseâ conversion.
If you are not using Windows but Linux install the plugin exactly as above. But you need to separately install opencc.
If you are using macOS you are out of luck for now 