IT, the question "how do we define nepalese culture?" is very tough to answer as it usually turns out to be "my culture" whoever attempts to put specific answerto this question rather than "nepalese culture". 

Back in home, during my first few months of schools in Kathmandu valley (mid 80s), I met many people who could not communicate with me in Khas-nepali language - the only language I learnt in my childhood. The "nepalese culture" I saw there was quite different culture than the "nepalese culture" I saw before coming into the valley.

Fast forwarding to my first two years of college (around 90s), a friend from Bardiya told one day - "If possible, I want to burn all the history book I read and all the knowledge of history of Nepal." All of us were surprised first, and thought probably he was anti-national element (arastriya tatwo) that the radio of the time used to iterate day and night. We asked cautiously - why? - "The history is only about Kathmandu Valley, Gorkha and few of its neighbors. Where is my Bardiya in the entire history? I don't feel this history is worth to read for me." Since then, I started to think of diversity and the jeal of self-recognition of the excluded people which did not come out but were somewhere burried heavily under the domination of unitary system.

Fast forwarding to my life in foreign country as a student (late 90s), I had to join a home-stay program with a family at a remote village, who chose to host nepalese student. The host family prepared vegetarian cuisine for me, and surprised me with a lot of questions about Nepal that I never knew. The reason was they had hosted a nepalese student the year before, who happened to be a strict vegetarian guy from eastern Terai who changed DHOTI everytime before his meal. That family had run into trouble to feed him because finding edible vegetable was hard in that village. The vegetarian guy probably tried to show them the "Nepalese culture" of changing DHOTI before meal. This year they were better prepared to host a nepalese without considering that Nepalese people might have quite contradicting culture. Whatever they learnt about nepalese culture from the guy was not in my knowledge. This put all of us into confusion. After learning briefly about their past experience, I tried to explain about the diversity in Nepal, different religion, different ethnicity, etc. When I told them we have more than 60 spoken language, they did not believe me. They asked - "is it different language or different dialect?"  "No, no it is not different dialect, it is different language, completely different sets of vocabulary, different grammar, and different accent." They immidiately asked - "how big is Nepal?" "Well it is small, but we have diversity." They asked - "Then, how do you survive? Don't you have problem to communicate? Don't you have wars?" - "No we have no problem because most nepalese can speak more than one language, and they know how to find the way to communicate even if they don't know the language." I tried my best to give more general version of Nepalese culture but I knew I was far from perfect or near-perfect explanation as I also might have talked more of my culture than real Nepalese culture. I started to realize then that nepalese people started to try exposing their own culture beyond the boundaries of "daura suruwal kot topi", "ek bhasa ek bhesh, ek raja ek desh", whenever they got the opportunity.

Fast forwarding to recent days - where the issue of nepalese culture and diversity is almost at the central of all political agenda and ongoing conflicts. The hot issues and debates on federal restructuring is basically focussed on how to recognize the diversity. The problem and solution approach restructuring new Nepal is based on addressing the concerns brought up by the diversity. Recently, Tamangs, Kirats, Magars and Newars had decided to unilateral declaration of autonomous regions and cash out the uniqueness of their cultural existence for claiming political right. Those groups, who feel they have unique culture to show and preserve, want to have autonomy, but those, who don't feel they have significant culture, want to envelope everything within a common term of "nepalese culture". 

So, I believe, there is not a clear answer of the question IT has put here. We need to wait some time until the dust of federal resturing settles down before getting somewhat clear picture at the earliest.