CKEditor language files contain entries for the scayt plugin, where options from the SCAYT dialog are translated, e.g. in German language file there is:
scayt :
{
title : 'Rechtschreibprüfung während der Texteingabe (SCAYT)',
opera_title : 'Nicht von Opera unterstützt',
enable : 'SCAYT einschalten',
disable : 'SCAYT ausschalten',
about : 'Über SCAYT',
toggle : 'SCAYT umschalten',
options : 'Optionen',
langs : 'Sprachen',
moreSuggestions : 'Mehr Vorschläge',
ignore : 'Ignorieren',
ignoreAll : 'Alle ignorieren',
addWord : 'Wort hinzufügen',
emptyDic : 'Wörterbuchname sollte leer sein.',
optionsTab : 'Optionen',
allCaps : 'Groß geschriebenen Wörter ignorieren',
ignoreDomainNames : 'Domain-Namen ignorieren',
// ...
However if you check the options dialog, strings from the language file are not used (for example ignoreDomainNames). See the attached screenshot.
CKEditor language files are used for localization in dialog window now.