Flask pybabel with SubmitField not allowing spaces in string

Question

I have a pretty complex Flask site using Babel for multilanguage support in templates using {{_('sometext')} It all works well except the buttons which truncate with any spaces in the string.

Example

         <h2>{{ _("Hello World") }}</h2>
    
         <input type="submit" name="h"  value={{ _("Hello World") }}>

This displays with the button text truncated at the space. Looking at rendered page source, I see the HTML below is malformed.

<input type="submit" name="h" value="Hello" world="">

Any idea how to allow spaces in Babel computed button values?