Re. the Whorfian hypothesis: Are there concepts or ways of saying things in one of the languages that you speak that can not be said or expressed or the meaning changes in another of your languages? How do you address culture in your classrooms? Do you go beyond the "holiday" model of culture?
Part 1: There are things that can only be expressed in one language, because so much of the language we get is built around the culture of the community in which it is spoken. When I began to truly understand (not just memorize) certain idiomatic expressions or deeply felt adages in Spanish that would only be relevant, say, in that part of Mexico, I was sooooo thrilled--it felt like I had arrived. It really spurred on my motivation and eagerness to learn Spanish even more. A classic example of this is the expression you hear all over Mexico (and other Spanish-speaking countries) of "Si Dios quiere..., which can be literally translated as "If God wishes." However, in the cultural context, it represents the religiosity and the fatalism inherent in the culture, so the literal translation loses its power and its intent to some degree if interpreted with a U.S. mindset.
Another one is one we've all probably heard, about how many (MANY! MANY!!!) words the Alaskan natives (Inuits? Aleuts?) have for snow. It would make absolutely no sense to someone from South Texas, who may have never even seen snow, but if you look at snow all day, nearly very day for most of the year, in every size, shape, different strengths of storm or flurry, well, of course you would have a lot of words to distinguish each type of snow/snowflake/snowstorm, yes?
Part 2: I am always looking for cultural activities for the classroom, ways to allow students to make the most of their natural resources of language and culture, and ways they can share these ideas. It helps when students come from different cultures within one class group to have them learn about each other, so each student feels valued and respected, and so they begin to understand each other better.
One thing it took me a while to learn to respect (as I have seen with other teachers, too) is the concept of a wait time before speaking that is prevalent in many Asian cultures (for example). Although to communicate effectively with, say, a U.S. businessman, you must eventually learn to speak up and reduce the "dead air" between utterances, these students have numerous reasons for waiting, all of which sound really good. Instead of just filling the empty space with nonsense words, unnecessary repetitions, or chit chat, many ELLs come from a culture of listening, then thinking, then speaking. And when you add the time for students to formulate a grammatically correct sentence to get their point across, well, we are looking at some serious wait time.
We should vary activities so that the more reflective or introverted students or students from a "high culture," where much of the communication is based on non-verbal cues and culturally understood traditions have an equal chance to participate. When we want them to jump in, think quickly, or interrupt each other, we should let them know that this is what is required for that activity, but that there will be other opportunities to communicate in the fashion of their preference and cultural conditioning. Once I realized this and learned to incorporate the wait time, I reminded the teachers that I worked with, trained, and managed not to fill in the spaces between utterances (a very common tendency for English speakers from many western cutlures). It is a struggle for many of us, but it is worth the effort.