You can't compare fixing some quadratic time behavior in one place (the type checker) to something that sounds like could be a major piece of work: multilingual character support in UI. If it only goes to ISO latin, it's probably using 8 bit strings, and assuming that bytes and characters are 1:1.
Also, the average Haskell developer practically exists for the purpose of fixing quadratic behaviors in type checkers; you file that bug at 3 a.m. on December 25, and by 8 you have a shiny fix under the tree.
The code I've asked contains two calls instead of one, aside of that it was quite simple and would allow at least Russian users of Clean to have proper dialog titles.
I guess it is nothing like "major piece of work". It was a fix for peculiarities of Windows UI of that era - dialog titles required different approach than dialog fields.
Also, the average Haskell developer practically exists for the purpose of fixing quadratic behaviors in type checkers; you file that bug at 3 a.m. on December 25, and by 8 you have a shiny fix under the tree.