I’m late to this party but you might find unicode_transform useful. Its a rules-based transliterator which implements currently just a few of the many CLDR transliterations. Equally it might be both too much and too little for what you need.
The transformation rules for Latin to ASCII are quite comprehensive!
@jayjun’s excellent slugify package would be my general recommendation for slugification.
Examples
iex> Unicode.Transform.LatinAscii.transform "ü ø ß"
"u o ss"
iex> Unicode.Transform.LatinAscii.transform "árboles más grandes"
"arboles mas grandes"
iex> Unicode.Transform.LatinAscii.transform "Übel wütet der Gürtelwürger"
"Ubel wutet der Gurtelwurger"
iex> Unicode.Transform.LatinAscii.transform "Ł"
"L"