find-charset-region

find-charset-region is a built-in function in `C source code'.

(find-charset-region BEG END &optional TABLE)

Return a list of charsets in the region between BEG and END.
BEG and END are buffer positions.
Optional arg TABLE if non-nil is a translation table to look up.

If the current buffer is unibyte, the returned list may contain
only `ascii', `eight-bit-control', and `eight-bit-graphic'.