I recently noticed an issue with the CKEditor on XPages not being displayed for edit mode. The editor doesn't show up completely.
A quick glance using the developer tools showed a resource not being loaded and then causing an error:
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I am using English as my browser language (and also on the OS level) but I wondered why this particular resource was attempted to load, showing the particular UK version of the English locale file. Another check of my browser settings gave the answer:
The language was set to British English instead of the generic English. I guess this is a bug in CKEditor not being able to break down the specialized locales to a common resource file name, so it tries to load the file called like the locale, i.e. "en-gb" instead of just "en".
How to fix
This is simple, just remove or change your default language in your browser to the generic English package and the editor appears again.
There is actually a KB article for this scenario I wasn't aware of. HCL support provided the link: https://support.hcltechsw.com/csm?id=kb_article&sysparm_article=KB0105212