```
A straightforward and hopefully uncontroversial refactor to improve
consistency.
Move the decision whether to translate an individual error message
to where it is defined. This simplifies call sites: no more
InitError(Untranslated(SomeFunction(...))).
Make all functions in util/error.h consistently return a
bilingual_str. We've decided to use this as error message type so let's
roll with it.
This has no functional changes: no messages are changed, no new
translation messages are defined.
Also make a function static that can be static.
```
Backport of core PR19176.
The change to `kitchen_sink.cpp` is not ported since this file hasn't
been ported yet, but the compiler will make the change obvious when
needed.
Depends on D8650.