The demographics of my research group represents fairly well the demographics of my broad field: there are very few women (presently none), and a large number of international students from all over the world, many from different parts of Asia and a few from Europe. The fact that my group members are presently all male is not ideal, but, on the upside, I can look at cultural aspects of the dynamics without the gender component perhaps obscuring the conclusions.
Having people from all over the world comes with challenges. An important part of my maturation as an academic has been to handle these culture-related challenges as they arose in a fashion that I hope is clear-cut, fair, and inclusive.
For instance, occasionally I will have 2 or 3 people from the same country, and they tend to speak in their native language when at work, which excludes others from the conversation. Since conversations in the lab are first and foremost supposed to be work-related, and since the language of instruction at the University is English, I now explicitly require that all the conversations in the lab or office be in English.
In my opinion, perhaps the most important skill a foreign-born graduate student should acquire during graduate school in the US is excellent command of English. I have often been quite disappointed at the quality of incoming students' English (completely incommensurate with test scores): it is frustrating for them to take classes and for both the student and me to talk about research tasks. I therefore insist that students for whom English is not a native language work tirelessly on improving it, through English-as-a-second-language courses, reading a variety of literature (from technical to popular), watching US programming, and -- most importantly -- through opening up to become friends with native English speakers. Unfortunately, I have had a few students communicate, directly or indirectly, that they feel learning English is not really important, and they spend years without exiting the comfort sphere populated exclusively by their compatriots. This is quite saddening, because a technically excellent PhD student, who wants to work in the US but cannot speak English fluently, often becomes an unemployed PhD graduate. I have found a strong correlation between the speed with which a student's mastery of English ramps up in the first few years and subsequent technical productivity; I believe both are manifestations of a strong motivation to succeed.
Occasionally, there will be a clash in the lab. At one point in time, I had a very conservative and outspoken US student, with mediocre technical skills, tell one of my international students (a very mellow guy, very technically strong) to "go back to [the student's country of origin]" after the latter student challenged the former one on a technical issue. I have had a situation or two where global politics was discussed in the lab and passions ran high; one of my explicit instructions nowadays is that I will absolutely not tolerate arguments about world politics or religion in the lab.
There are also some amusing (at least in hindsight) aspects of diversity, where diversity should be interpreted in the broadest sense (i.e., not as US vs non-US folk). For instance, some of my lab/office rules now include explicit instructions on proper food storage (e.g. food should be stored in the fridge and not left out to rot on one's desk for days) and hygienic habits (frequent showers and washing laundry). This sounds silly, but I have had more than one occasion of a student with a strong body odor (these were sometimes local and sometimes international students, all with various backgrounds), where the smell was so strong that it would disrupt the work of others to the point of them avoiding to come to the lab after complaining in vain. Not only am I now well versed in conversing about someone being stinky (which used to haunt me as possibly the most uncomfortable conversation ever), I have had to occasionally do it more than once, and in one case, after repeated conversations, I had to threaten termination of research assistantship unless the situation improved (it did). I have also talked with students about laundry issues such as fabric softener choice, and I once researched Al-free deodorant for a student who would not use any deodorant for fear of cancer. I remember thinking whether this was really part of my job description as their research advisor, but I suppose it is, because I see no one else volunteering...
But, challenges aside, having a culturally diverse group is much better than having a culturally uniform one. For instance, often I have students who have excellent technical training but have been schooled in a system where initiative and independence are discouraged; I have others who are very independent and creative, which their school system fostered, but may lack, sometimes significantly, in math and physics skills. Together, the mix enables all of them to become much better young researchers overall, as they learn from each other.
It has also been quite heartwarming to see how friendships forge, sometimes between people whom you would never expect to bond, with origins very remote from one another. It is interesting to see how often students who are good friends end up coming up with very original research ideas; I have had several student-initiated papers, where it was always two students, from very different backgrounds, who became good friends in grad school and came up with an idea that meshed their expertise and resulted in cool new science.
In my opinion, getting to know one person from a certain cultural background really well has the ability to bring the whole culture much closer to you than any touristy trip ever could. Personally, I certainly have a much better appreciation for the cultures of several countries after having advised students from there. Our foreign students and postdocs are their nations' great ambassadors in the US and on the global scene. At the same time, our local, but culturally and racially diverse students, bring about the best of the US into global science.
What is your favorite anecdote that illustrates the joys or challenges of working with a culturally diverse research group?