Just recently I tried soldering a Japanese coin to sterling silver,
and it worked. I don’t know what metal the coin was, but it had a
similar weight and appearance to American nickles.
I used regular silver solder, liquid flux, and a propane torch (my
attempt at keeping the temperature low to prevent the coin from
melting, since I still don’t know exactly what type of metal it is).
I sweat-soldered the whole thing, and came out looking quite nice
for an experimental attempt.
For pickling, I used an old coffee mug to scoop up some hot pickle
for the coin/sterling silver to sit in all by itself (no worries
about contamination, and a good way to recycle coffee mugs that one
would otherwise throw away). The coin did become slightly
discolored, quite similar to a coating that nickle-silver can get,
but it came off without much work at all.