See https://stackoverflow.com/questions/720052/nslog-incorrect-encoding.
The `%s` format placeholder for `NSLog()` expects an encoding other than UTF-8, which leads to garbled Unicode characters when trying to print a UTF-8 encoded string.
```Objective-C
NSLog(@"Ä %s %@", "Ä", @("Ä"));
```
prints `Ä √Ñ Ä`.
As can be seen in the example above, the workaround is to convert the UTF-8 encoded C-string to an `NSString` object and print that instead.
`debug_key()` calls `NSLog()`.
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