Answer:
It is important to define what we mean by "culture" and "identity." After a bit of reading and thought, I came up with this working definition of the first of these concepts:
"Culture. The collective ideas, values, and patterns of behavior of a group of people; culture consists of a set of intertwined subsystems, the generally blurry borders of which do not necessarily coincide; these cultural subsystems are transmitted and learned, and are constantly adapting to the changes in the geographic and social context of the group."
These cultural subsystems include things like economic strategies, social organization, material technologies, music, dance, visual symbolic systems, verbal symbolic systems, etc. Thus language is but one aspect of culture, intertwined with these other aspects.
If you were to construct a three dimensional graphic model for plotting the distribution of cultural subsystems throughout space and time, then place within it data from groups of people living in some concrete geographic and chronological frame, you would probably find that each subsystem has distinct, blurry and overlapping boundaries. In some cases there may be no overlap at all. The complexity of the situation makes it difficult to make a clear association between language and other cultural subsystems, since these do not line up along neat boundaries, like those of political maps, which give us an extremely limited vision of human cultural complexity.
Ethnic identity is a separate but related matter. Language may be an important factor in defining ethnicity, but it is not the only one, nor is it a necessary component. Any cultural subsystem, or combination of these, may come into play. An individual's or a group's ethnicity is flexible and may change in a short span of time, as a response to a changing social and cultural context, and to internal processes of transformation. Nationalism may be thought of as a sort of macroethnicity, usually invented and imposed upon a population by a nation state.
Step-by-step explanation: