Language setting has no bearing on available loot - PROOF
Anyone with a basic understanding of client-server architecture and access to two devices connected to the same account can see clearly that changing languages will not affect the potential loot you can find when searching for a raid.
It's extremely simple:
Log into your account on device A and change your language to Chinese, and log off.
Now, log into device B. You will see that the language setting you selected on device A has no effect on device B.
You can do the same thing with music and sound effects with the same result.
What this means is that client settings (language, music on/off, sound effects on/off) are stored on the client, not the server.
Furthermore, every base you come across on a raid search is a base of someone that is offline. If the language setting is stored on the client only, what function would cause them to be placed in a queue in which only devices with a certain language setting would be able to find them?
Myth debunked :)