It is completely acceptable to display this kind of information on your CV and I can't think of any situation where it can hurt you professionally or socially. However, I would not recommend putting this kind of information on the resume you send out for specific positions (or even proposals) unless it is important to the job (or proposal) you are applying to.
I say this because your CV is a more complete profile of your professions and abilities and listing another language (preferably near the bottom somewhere above hobbies) will not be deemed as a bad thing and in many cases it can actually have a positive effect on how others perceive you. However, a resume is more tailored for specific needs and listing irrelevant information can always have a negative impact on the opposite person.
EDIT: In my personal line of work/study (computer science), speaking another language usually does not help you directly, but is is seen (by many) as an indication of your potential abilities. Speaking another language (and speaking it well) is not an easy task and those who are capable of doing so, show above-average motivation and determination.