it's obvious isn't it? it's like "if you can't learn calculous I'm pretty sure you haven't the skills to do rocket propulsion calculations"
Someone with only one language or a "main language" is someone who just simply has a lower level of skill than is needed for embedded programming- which requires lots of different skills and languages. Being able to learn more than one thing is a prerequisite.
if your natural response to something like embedded php is "Oh how convenient, I can use my main language!" then that would imply the answer is "yes", since, if you do know other languages your natural impulse would be to use pretty much any other language if you have a choice.
Someone with only one language or a "main language" is someone who just simply has a lower level of skill than is needed for embedded programming- which requires lots of different skills and languages. Being able to learn more than one thing is a prerequisite.