This app supports multiple languages (English and Chinese (simplified ) ) , if any user is having such problems try these steps , uninstall the app and see what your phone regional settings are set to and then try to re-install the app from this link
Yuki FileExplorer | Windows Phone Apps+Games Store (United States) , if issues still persists uninstall the app, go to your desktop/Pc and download the xap file on your computer from the same link. Cop the xap file to the root directory of your memory card. reboot your phone and let store notify you to install app from sd card by going into windows phone store.