Are you expecting to find many French words together, or are you looking for loanwords? It seems like loanword detection is an
open research problem, but if you're up for writing a bit of code, I found a few options for doing general language detection:
If you are comfortable with Python, then
langdetect (a port of
this Java library, if you prefer Java); a similar option implemented as part of the spaCy NLP framework,
spacy-langdetect; and
textblob (which appears to farm out the language detection to the Google Translate API).
Langdetect seems nice and simple, but you still need to figure out how to walk over the words in your book, so spaCy might be a better choice for that, as it comes with
sentence segmentation.
Good luck!
