Are you new to game development?
Game developers don't typically license their games. They would license their tools if they choose to make it available to the public. There are many free game-development tools available on web, ranging from one specific aspect (e.g. graphics, sound, physics engines) to a whole "game-maker" package (e.g Unity, Unreal).
The tools help you to make games, but it means that you still have to develop the games yourself. Developing games include writing the code for it, adding the graphics and animations, adding the sound effects and music, and adding the game elements. In your case, you know that the game will involve learning vocabularies. How do you design your games that your players can learn vocabularies quickly? What are the vocabularies to be learned? How quickly do you want your players to progress from one level to another. All of this must be thought out.
You want to make 50 of these. How do they overlap? How do they differ?
It's a LOT of work.
If you ask, why can't I just license Pacman or Breakout, and just add vocabulary elements to it? The thing is, when you add one extra feature, it will end up with a whole different game. Different code, different graphics, different mechanics. Let's use board games as examples, how do you add poker to Monopoly? The rules would have to change, wouldn't they? When the rules change, it's a whole different game.