When I install Drupal 8 in English and set it to any RTL language, CKeditor stucks in LTR mode; The whole editor will appear flipped (and even right ctrl+shift won't change the cursor to the right, nor it would help much if they did).
The editor will appear RTL only if I turn on the "Interface Translation" module. This is problematic since it forces Hebrew translation to my whole management-interface into Hebrew, and I don't want that because I have 1001 reasons to keep my management-interface in English.
The solution for this problem, which I believe should be part of the next release, is to make "Interface translation" redundant for CKeditor RTLness in Drupal 8 --- I'm sure we have only reasons to do so and no reasons not to do so - We shouldn't force people to auto-translate their management-interfaces to languages other than English: It can sometimes be impractical and annoying and not everyone desire that.
Since I only learn to program, and far from being able to fix this now, I kindly ask the core maintainers to take care of this problem.