In an Asian massage parlor, it is perfectly acceptable to speak as you would in any other massage parlor. Always use respectful language and do not be overly friendly in speech or in gestures as it may be considered improper in many Asian cultures, according to China Highlights.
If the massage therapist speaks limited English, speak in a clear and concise manner and repeat what was said if needed. It is customary for Japanese women to use Teineigo or the polite form of speech when addressing strangers, according to Japan Reference. In a massage setting, your therapist may downplay or even criticize their massage skills. This is often customary in Asian culture where humility and respect are admirable qualities.