How to perform a for loop on each character in a string in Bash?

I have a variable like this:

word="Hello!"

I want to make a for loop on each of the characters, one at a time, e.g. first character="H", then character="e", character="l", etc.

The only way I know is to output each character to separate line in a file, then use while read line, but this seems very inefficient.

• How can I process each character in a string through a for loop?

With sed on dash shell of LANG=en_US.UTF-8, I got the followings working right:

$ echo "你好嗎 新年好。全型句號" | sed -e 's/\(.\)/\1\n/g'
你
好
嗎

新
年
好
。
全
型
句
號

and

$ echo "Hello world" | sed -e 's/\(.\)/\1\n/g'
H
e
l
l
o

w
o
r
l
d

Thus, output can be looped with while read ... ; do ... ; done

edited for sample text translate into English:

"你好嗎 新年好。全型句號" is zh_TW.UTF-8 encoding for:
"你好嗎"     = How are you[ doing]
" "         = a normal space character
"新年好"     = Happy new year
"。全型空格" = a double-byte-sized full-stop followed by text description