As the Globalize.format() function always returns a '.' decimal separator, as far as i understood, there is a little hacky solution, but at least it works. The point is at replacing the 'neutral' decimal separator with that for the current culture
Globalize.parseFloat("1.2435677777", 10, "en-US").toString().replace(".", Globalize.cultures[Globalize.cultureSelector].numberFormat["."])