Is your feature request related to a problem? Please describe.
No

Describe the solution you'd like
A way to change the language of the yelled out warning messages without changing the client language.

Describe alternatives you've considered
Instead of implementing a option in the interface. A guide in the wiki what files to edit.

Paul is right. A lot of stuff is auto localized. Generic names are being used more in some places (like retail due to encounter bloat) but even that is problematic because we only have 3 maybe 4 consistent localizers and if you need to localize almost every spell manually instead of auto from GetSpellInfo, it's tons of additional work and time investment that I frankly don't have. It's why even then I only use custom short localizations sparingly.

This is why this feature request just kinda sits on backburner forever. Unless blizzard adds some tech where we can request a diff localization return from spell names than what client is set to, I don't see it changing much either.

As someone playing on an EU server that is indeed something that I've looked into before. Unfortunately it's non-trivial because a lot of the text like spell names etc just come from the game itself, so the other language options just aren't available anywhere :(

However, what I think is a good idea would be using fewer spell names and more generic terms.