Spell checking the OCR text layer requires that you run WebDjvuTextEd on a webserver with PHP support and PHP needs access to the spell checker engines. The editor works without using a spell checker too.
The spell checker backend supports two engines: Enchant and PSpell. Since Enchant is just a wrapper to other spellcheckers, you can use hspell, aspell, ispell, myspell...
Make sure to install the necessary PHP modules, spell checkers and language packs on your server. You may need to check the documentation of jquery.spellchecker. (Note: this project is currently not maintained, so install this part of the DjVu editor on your own risk.) Ubuntu examples:
apt-get install php-pspell aspell-hu
or
apt-get install php-enchant hunspell hunspell-hu
The PSpell backend cannot query the supported languages, so it will present a text input box to enter languge code. The help users to choose, you must create a text file in webdjvutexted's /spell directory using this:
aspell dicts >aspell_dicts
There is also a little debugger script for Enchant setup, call this file from the WebDjVuTextEd installation to show info. Note that this file is not necessary for the normal operation, so you may decide to not install it on your server.
/spell/langs.php