I wasn't under the impression all the Younglings understood Byph and Gungi. I think it would be normal to pick whatever language you want to learn as a Jedi and learn it. Not to mention the Jedi is kinda a multi ethnic/ race organization and they might pick language and cultural stuff off of each other just from being friends and teaching each other so long as they were old enough to speak by the time being taken. Ahsoka looked like a 3 year old in the flash back, old enough to have basic language skills. Even so it seems like the Jedi encourage their ranks to be somewhat true to there roots. Makes ense to me. This isn't so different from how I've picked up some Persian phrases because one of my best friends IRL is from Iran.