If the handwriting recognition shows a wrong default language, please tap the Gear icon in the top-right corner of the Library view > Settings > Handwriting Recognition > Default Language, and check whether your language settings are correct.
If the issue remains, you will need to change the language for the particular notebook. Tap the Search icon near the top-left corner of the document view, type some text, then tap the language text at the bottom of the Search popover and change the language.