Change WebYep editor settings

I’m implementing WebYep CMS on a site. All works fine, but when using TinyMCE, its interface is in English.

I’ve also tried CKEditor which has the interface in Dutch automatically, but lacks settings for h4 and h5.

Does anyone know how to change TinyMCE’s interface to Dutch or add settings for h4 and h5 to CKEditor? I’ve looked around in the webyep-system folder, but can’t find it.