If you are wielding a two-handed weapon (versatile or not), and want to pull out a javelin and throw it, you don't need to drop the two-handed weapon, just switch your grip.... but.... at that point you are holding the two-handed weapon in one hand. If you want to wield the two-handed weapon you'll have to drop the javelin.
The off-hand property only pertains to attack powers and class features that ask for that keyword.
Any PC, not just a Ranger, can hold a long sword in each hand, and as long as they only attack with one, or the other, they suffer no penalty (they don't get the proficiency bonus if they are not proficient, blah blah bald). They just can't use powers that allow you to attack with both weapons, as they all (iirc) require that one of the weapons be off-hand.
The crux is the word wield, which implies you are using it to attack. Carrying and/or holding, are not wielding.