The CKEditor provides some ways to customize the look and functions. Answers to questions should always be searched in the documentation for the CKEditor because the editor is an own project. Here are just some examples that directly affect Kunena.
The path to the CKEditor configuration file is /media/kunena/core/js/ckeditor_config.js This file can be customized like remove buttons or add other languages etc… To ensure that these custom settings are not lost during an upgrade, add a prefix to the configuration file like “custom”. From ckeditor_config.js to customckeditor_config.js
Now go in the backend to Kunna -> Templates -> Your Kunena Template -> (tab) BBCode, scroll down and enter the prefix into this field (see image). After empty the Joomla and browser cache, the custom file will be used.
On the add-on page of the CKEditor project you find several skins for another editor layout. You see a preview on it, if you click on the name of a skin. Download your favorite and unzip the file. Open the folder and copy the contained sub folder to /media/kunena/core/js/skins
Now go in the backend to Kunna -> Templates -> Your Kunena Template -> (tab) BBCode, scroll down and enter the name of the skin into this field (see image). After empty the Joomla and browser cache, the new skin will be used.
Sources: The most of these procedures have been found at CKEditor 4 Documentation and CKEditor Forums and all credit for the solutions goes to the original authors. These procedures have been supplemented and adapted for use with Kunena.