Can I online-play a game purchased on one account when logged into another account set to a different locale?
Solution 1:
Yes
For games, 'Main' or 'Secondary' accounts can buy/download it and the game will be available for all accounts on the same PS4 system. With any account you download the game, you'll be able to play it on every account of that same console (no matter where it says it's located).
What you can't do is buy the Plus subscription on a secondary account, because it will only work on that account and on none other even on that system.