The gate latch needed an opener for the other side. Has needed for a couple of years.
After some thought, I decided to use a bicycle shift cable that was plenty strong for this application, but had some minor damage that made me not want to put it on a bike. Putting the shift cable in a left-over piece of housing allows someone to pull down on the cable from the other side, pulling up on the catch for the the gate and opening the gate.
I cut a piece of dowel to use as a handle and threw in a carriage bolt I had lying around. Perfect. I used CATV brads to tack the cable housing to both sides of the gatepost.
Except, there is a problem with these latches: if there is even a very small upward force on the attachment, it keeps the latch open, so that the gate never closes. The cable moves very smoothly in the housing, so even a very light handle will drag the latch open. So now the gate has an opener, but the opener kept the gate from closing.
I thought a bit, and realized the solution was quite simple: remove the brad holding the housing on the inside of the gate. The housing springs outward, pulling the latch closed. Pulling down on the handle on the other side pulls the housing towards the latch, then pulls the shift cable through the housing, opens the latch, and opens the gate.
It's probably lucky I decided to use shift cable and housing. Modern shift cable housing is quite stiff compared to typical brake housing, so brake housing may not have been springy enough to work.