Text editors

What file(s) should I look for if I would like to have the buttons and messages of the spell checker translated? I tried to translate the lib/editor/plugins/SpellChecker/lang/en.js into Czech, but to no avail.
Only later did I find out that the messages appearing on the screen are actually those in the lib/speller folder. But I can't see how to translate them. Am I missing something or are they hard coded really? (I'm using Moodle 1.5.2+.)
Thank you.