Thanks for the additional context! I see now that Loco Translate has some interesting logic. We’ll fix this in 1.0.5!
I also have found that BOTH are run from your plugin, which makes it slower.
Just having two files generated does not make them slower. Only one of them will be loaded. You can safely delete one if you’d like, but it also doesn’t hurt anything.
At last, I have some concerns about the secury of these approaches, since the po files which are downloaded automatically (and cant be stopped) are instantly converted to .php and run on each page load, which could have implications. What are your plans to make this approach as secure as possible?
There’s not really a security implication with this automatic generation. Any translation files are already trusted by WordPress, and the file conversion is just a convenience. Also, once we merge this into WordPress core, you’ll get the PHP files directly from translate.www.remarpro.com, mostly removing the need for the whole file conversion. That said, you can also completely disable the file conversion or PHP file usage in general using the provided filters.