Portable Ops exploit is for JP region only, and Mimina Lyar Chronicles has been pulled from all PS Stores. Mimina hasn't been pulled. You just have to buy it from the online store on your PC. Thanks, Teh Cupcakes!
Unless you really really like Remote Play and PS Now, in which case 3.55 is currently the one to have. My Slim on 3.55 hasn't been switched on in a couple of weeks though, so that's the extent of my opinion on a non-exploited console...
You just need to buy it from the web store and use the download list. Assuming you are able to purchase it (I purchased it a while back, so I can't confirm that still works), the exploit will work on 3.55.
The language setting has nothing to do with the region of a PSTV. You would need to register a US PSN account, then factory reset your PSTV so you can sign in to the US account. However, unlike the PS Vita, I hear that the PSTVs do have some region restrictions. I think the whitelists are region-specific, and are actually tied to the hardware's region rather than the PSN account's region. Thus, I'm not sure if an EU PSTV would be able to play US games... (Digital or physical.)