For now, if you want to load messages from for example DB, or other external source,
when you implement yours custom LoaderInterface class, an register is as a loader service, it shows that this doesn’t work out-of-the-box.

For example you register custom Loader aliased db; for that to work, you have to create a dummy empty file under Bundle's translations folder - for every domain and locale you have in DB:

• messages.en_us.db
• messages.pl_pl.db
• app.en_us.db

etc...

This is because Framework's Bundle omits loaders that don't use files

Fixing this will probably be a BC break, so before I post PR for that I want to hear some feedback :)