When:

1. adding a webhook with "comment added" trigger,
2. using a variable ${comment} on a custom payload, like: 
   {{{ "message": "日本語のキーボード", "variable": "${comment}" }}}
3. I add a comment with the following text: { "message": "日本語のキーボード", "variable": "日本語のキーボード" }

Then: 

1. A webhook is called with an invalid payload, like this:

{ "message": "日本語のキーボード", "variable": "

{ "message": "日本語のキーボード", "variable": "h1. 日本語のキーボード  " }

"
}