Previously as soon as any override was defined we would regress to the slow
path for locale lookups. Additionally if `raise: true` was specified which
rails likes to add in views we would bypass the cache
The new design manages to use the fast path for many more cases
This change both speeds up specs (less strings to allocate) and helps catch
cases where methods in Discourse are mutating inputs.
Overall we will be migrating everything to use #frozen_string_literal: true
it will take a while, but this is the first and safest move in this direction
