I mean, he goes into some detail about the issue: he wants to be able to use an internationalisation library, but the best option is in javascript, and these libraries are very hard to write because i18n is really hard with a bunch of edge cases. He also gives evidence that some commercial apps using Elm really need this functionality. He wrote bindings so it could be used in Elm, it worked well, but the core team were not interested in his solution, seemed to misunderstand the problem, and will not allow anyone else to solve it without an outright fork (which the core team act extremely hostile towards).