Why am I unable to install any kind of app on my BlackBerry OS 10.2.1.3412?

Sir please help me, I am not able to install any app neither from external sources nor from blackberry store. It's showing error installing app and "utf8 codev can't decode bytes in position. This error is also after secure wipe, Sir please reply to me as soon as possible, I have to download an very urgent app. Sir please help me. Please. I will be very thankful to you

Despite the sexist salutation, I shall suggest an OS reload through Link or an autoloader.

As you are on 10.2.1, either you haven't received the upgrade or you have chosen to stick with 10.2.1. If it's the latter, you will have to choose an autoloader for the process.