Firstly: I have no idea why this happens.
I have tried to switch my application into production mode by modifying bootstrap accordingly. After reload all the translated strings were gone, replaced by their placeholders used in the code. Purging the cache solves the issue and further prod/dev modes switching doesn't affect translation anymore. And so I'm unable to reproduce the issue.
Still, I think this should be reported as a bug if not for fixing, than at least for awareness that something like this can happen.
Firstly: I have no idea why this happens.
I have tried to switch my application into production mode by modifying bootstrap accordingly. After reload all the translated strings were gone, replaced by their placeholders used in the code. Purging the cache solves the issue and further prod/dev modes switching doesn't affect translation anymore. And so I'm unable to reproduce the issue.
Still, I think this should be reported as a bug if not for fixing, than at least for awareness that something like this can happen.