I object to this special snippets. You can autodetect if the space is needed or not, right?

~~~~
has_cjk = lambda char: len(re.findall(r'[^\u4e00-\u9fff\s]', char) != len(char)
~~~

Than you can have

~~~~~~
snippet sc "Strong string" w
`!p snip.rv = r'\ ' if has_cjk(t[1]) else ''`**${1:${VISUAL:Strong}}**`!p snip.rv = r'\ ' if has_cjk(t[1]) else ''`$0
endsnippet
~~~~~~

and similar for the other snippets. I have not tested this, put it should work, or not?

But please add an comment for other users :)