Strange looking image input box

Hello,

I'm using the latest release of the TinyMCE 5 module. Something goes wrong when I try to input an advanced image.
I use IMCE integration for searching and uploading images to the user account. There for I press the button to the right, and an extra pop-up opens.

What I'm wondering about is the way this image intergration interface looks like. Notice the strange text labels and buttons.

Does anyone know this problem? Thanks!