Are there any rules on the Visibility / Audibility of spellcasting?

Can a wizard chose to cast without gestures and/or arcane incantations? Were there any rules for this in 1st and 2nd?

Fresnel said:

You can always add misfortune or challenge dice for doing so, but no official rules as far as I know.

Not sure, but the closest thing I could find in the RAW would be to make the casting/invoking an opposed check vs the observation of the person/people you are try to hide it from. No this isn't perfect but its the closest thing I could find without making up any new rules.

In v2 the wizard needed to be able to speak (using an Arcane Language).

I dont remember it being explicit in v1, but most of the art shows gestures and the like (and it still had the various Arcane Languages).

As the arcane languages were such a feature of earlier editions, I would say that speaking the spell seems more important than any gestures.

Was the need for 'Arcane Language' a mental tool to help construct and guide the spell or were the sounds made necessary for the spell (or both)?

If it is just a mental tool, than it might be possible to just speak them 'in your head' - this might up the difficulty 1d. If loud incantation is always necessary then it limits some opportunities. I have been imagining Grey Wizards casting silently in needed. Maybe the official fiction might shed some light on this?

My house rule is that spellcasting requires verbal commands to focus your mind and hand gestures to focus your energy and target. You can cast without either one of those for 1 additional challenge die, or without both for 2 additional challenge dice.