East Asian wide characters with combining diacritics:

中文 [combining low line]:
中文̲

xxx中[combining low line]文:
xxx中̲文

Overwriting an East Asian wide character with combining diacritic with an East
Asian wide character without combining diacritic, in the middle of an 80-column
line with mixed narrow and wide chars:

xxx[...]xxx中文[combining low line]xxx[...]xxx你好ESC [ 23 G 国:
xxxxxxxxxxxxxxxxxxxx中文̲xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx你好国

xxx[...]xxx中文[combining low line]。xxx[...]xxx你好xESC [ 23 G 国:
xxxxxxxxxxxxxxxxxxxx中文̲。xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx你好x国

Overwriting an East Asian wide character with another one with a combining
diacritic, in the middle of an 80-column line with mixed narrow and wide chars:

xxx[...]xxx中文xxx[...]xxx你好ESC [ 23 G 国[combining low line]:
xxxxxxxxxxxxxxxxxxxx中文xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx你好国̲

xxx[...]xxx中文。xxx[...]xxx你好xESC [ 23 G 国[combining low line]:
xxxxxxxxxxxxxxxxxxxx中文。xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx你好x国̲

Overwriting a narrow character with an East Asian wide character with a
combining diacritic, in the middle of an 80-column line with mixed narrow and
wide chars:

xxx[...]xxx中文xxx[...]xxx你好xESC [ 25 G 。[combining low line]:
xxxxxxxxxxxxxxxxxxxx中文xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx你好x。̲

xxx[...]xxx中y文xxx[...]xxx你好ESC [ 23 G ，[combining low line]:
xxxxxxxxxxxxxxxxxxxx中y文xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx你好，̲

Overwriting a narrow character with a combining diacritic with an East Asian
wide character, in the middle of an 80-column line with mixed narrow and
widechars:

xxxxxxxxàxxx[...]xxx中文xxx[...]xxx你好xESC [ 9 G 中:
xxxxxxxxàxxxxxxxxxxx中文xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx你好x中

xxxxxxxxàxxx[...]xxx中文xxx[...]xxx你好xESC [ 8 G 中:
xxxxxxxxàxxxxxxxxxxx中文xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx你好x中

Overwriting an East Asian wide character with combining diacritic with a narrow
character without combining diacritic, in the middle of an 80-column line with
mixed narrow and wide chars:

xxx[...]xxx中文[combining low line]xxx[...]xxx你好ESC [ 23 G y:
xxxxxxxxxxxxxxxxxxxx中文̲xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx你好y

xxx[...]xxx中文[combining low line]。xxx[...]xxx你好xESC [ 23 G y:
xxxxxxxxxxxxxxxxxxxx中文̲。xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx你好xy