Yep 100% yes even if its a made up language that only the creator knows yes period anyone that says no is just wrong or is using house rules, but if they are not speaking it its more likly itll be a random language they know until they say somthing in druidic then you may elect to speak druidic
As a DM yes it would...even if the language was some crazy hermits made up nonsense that only he knew but was a language made by an "intelligent" creature a oesron with the active tounges effect would not only be able to understand the language bit its meaning too ans well as speak it back in...