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Proposed wording looks superfluously verbose to me.
Look also at description in Include/unicodeobject.h:
/* Translate a string by applying a character mapping table to it and
 return the resulting Unicode object.
 The mapping table must map Unicode ordinal integers to Unicode
 ordinal integers or None (causing deletion of the character).
 Mapping tables may be dictionaries or sequences. Unmapped character
 ordinals (ones which cause a LookupError) are left untouched and
 are copied as-is.
*/
It is repeated (more detailed) in Doc/c-api/unicode.rst. Isn't it pretty clear?