Here's my DIY guide how to fix "mb_internal_encoding()" error.
- Login to WHM and search for EasyApache and click on EasyApache (Apache Update)
- Click Start customizing based on profile
- Keep the Apache Version the same and click Next Step
- Unless you need to update don’t change the PHP Version and click Next Step
- Skip the Short Options List so press Next Step
- On Exhaustive Options List, Search (Ctrl+F) for Mbstring and check ✓ it
- While your there make sure you have GD, FreeType, Iconv, cURL and Zip checked
- Press Save and Build
- Check yes to Recompile Apache and PHP and select I Understand
- Build time takes about 10-15 minutes and your done!