I do like the idea of a switch outside as it has a lot of benifits.. Perhaps I am overthinking things by adding a "wireless" switch and instead could just put an external light and convert to 2 day as you suggest... I am going to look into that as an option.... My only reistance is that this face of the garage get hammered by the weather... All of the fittings and fixtures on that side are ruined.. So i worry about water ingress.. But I guess if the back box is sealed against the wall and the switch/box is IP66 rated, I have little to fear.
As you say, probably OK -although anything electrical exposed to elements is somewhat of an 'uncertainty', even if allegedly IP66!
As an aside, if it were my house, I might be thinking rather 'laterally' For a start, I might well consider ...
In that room I'd be tempted to just run surface conduit round to the other side of the door .....
If I didn't like that idea (presumably only because of appearance), and if I were worried about water ingress into an 'outdoor' switch, I might consider changing the current indoor switch to some sort of 'push' one (push to switch on, push again to switch off), somehow mounted 'back to front' (push button facing wall) and then have some sort of (plastic/wood/whatever) 'rod' going through the way to some sort of button which allowed the switch to be operated from outdoors. In that way there would be nothing electrical outside 'facing the elements'. Probably too complicated/unconventional/esoteric for you - but a sort of approach which I might possibly consider! ... or even an 'internalpullswitch with the pull cord going through the wall9probably with pulleys)!
Another 'lateral thinking' approach might be to install a 'push to break' switch in the doorframe, wired in parallel with the existing light switch, such that the light came on whenever the door was open - which would enable one to enter the room and find the existing switch, even in the dark. However, that would mean that the light was already on whenever the door was open - but even that 'problem' could probably be addressed by "2-way switching".
Those are just a couple of examples which illustrate that, if you really want to, there are any number of 'unconventional' approoached which can be considered!
Kind Regards, John