I just installed Evernote Legacy, thanks for the link!
I understand the reasoning of the dev team. Using the built-in Windows spellchecker saves maintenance. I think you can change the language of the spell checker by installing language packs and enabling multi-language support in the Windows settings. However: there is a major bug somewhere; turning off spell-check in Windows has no effect on Evernote! This is a killer for many people, as not everybody types plain text in Evernote. For example: code.
Another tip is to use the web interface. There, spell-check can be disabled.