No but you can call the local municipality to advise them of the non-permitted work.
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Generally speaking, the tenant can sue the landlord for anything, but the tenant would not win a judgment for monetary damages unless the rental dwelling had health and safety issues which amounted to uninhabitability. The mere fact that the tenant suspects the lack of permit does not automatically render the dwelling uninhabitable.
Frank W. Chen has been licensed to practice law in California since 1988. The information presented here is general in nature and is not intended, nor should be construed, as legal advice for a particular case. This Avvo.com posting does not create any attorney-client relationship with the author. For specific advice about your particular situation, please consult with your own attorney.
I am not sure of the relevance that the landlord cannot speak English. However, if the landlord is your friend, perhaps the first step is asking the landlord to fix whatever problem exists and/or make sure the bathroom is properly permitted.
Further, I agree with my colleagues that existence of an unpermitted bathroom without more problems affecting the habitability of the rental unit probably does not support a claim for damages.