Can anyone tell me what this "LaserDisc" CARTRIDGES are?

Well, now you have a new addition to your bucket list.

Wish 13: I'd like to flash a multi caption card and use it within my lifetime.

 

These carts are only for scarce Chinese players. Laserdisc did officially get digital captioning in the mid 90s with "LD-G", which is probably similar to DVD overlay captioning, but personally I think it would have been better if broadcast captioning was more sophisticated. If more lines were dedicated to it than just line 21, many languages could be easily embedded in any video signal and it'd be up to the TV to decode them, very cheap.

 

I quite like the Stargate one

 

Agreed I have never seen a player with cartridge input (sans MSX of course if that counts), had a scout around on one forum there was one mention of an add on cartridge player, here is the quote:

"we even bought a subtitles cartridge player (forgot what its called) during the Laser Disc days. you can tweak the subtitles. colors, fonts etc."

 

See my previous Reply on page 1 with a pic
Maybe the Language Carts plugs in one of the Game Pak units or has it a separate "Language Module Game Pak?