Applying to CS for ML/NLP, will a recommendation from a professor not in CS be an issue?

[tanker11]

I'm applying for an Masters in Computer Science this Fall, looking to specialize in AI/Machine Learning and NLP. The main university I'm applying to (quite selective) requires three recommendation letters. While I haven't officially asked professors yet (looking to do that this week), I believe I have the possibility of two good letters:

(Side details: I did a double major in undergrad in CS and a foreign language (not English) at a top 25 university, very good GPA and GRE)

Professor 1: I took three undergrad courses with this person, including one that was small and focused, getting an A in each. He knows me really well as far as my academic capabilities and potential for research, as well as teaching ability (the specialized class was a mentorship-like course, helping project groups from previously taken courses accomplish them).

Professor 2: I did about 1.5 years of research supervised by this person (no classes) at a pretty prestigious research institute affiliated with my undergrad university. (S)he can definitely speak to my research ability and overall academic knowledge. I have two publications that were presented at a conference, though I don't know its academic reputation; these publications, while not directly ML/NLP combined, are potentially relevant, I think, involving statistical analysis of discourse patterns.

 

 --> Now, I'm thinking about asking this third professor, but I'm curious to see how this might be perceived:

Professor 3: I took two courses under this person. Both classes are in my foreign language major, and I received an A in each: one was an intensive writing course; the other was a semester-long research course, during which time I produced an honors thesis (this person was my advisor on this). In this thesis, although it was under the foreign language department, my focus was on machine learning (simple classifiers) on language models. I think s(he) can also speak to my research, academic, teaching abilities, and awards, overall providing a strong letter.

I'm curious on this aspect: while it may be a strong letter (#3), will it be viewed unfavorably in admissions for Computer Science because (s)he is not technically a Computer Science professor?

 

I view the case as strong for this letter due to NLP being my particular interest within CS, my interest in languages (like the one I majored in), and more research experience that both I and this professor can speak to. On the other hand, it seems like a risk.

 

Am I overthinking this, or is this potentially a bad idea?

 

Thanks for any of your help! (and let me know if you'd like more details - kept it a bit conservative to start)