This is an issue for non-latin wikis, the default asciifolding we use will only fold latin (ascii) chars. For some language such as greek it is useless.
Some language specific analyzers may provide better folding but those are not used by in autocomplete search.
We cannot integrate it as is because it lacks the //preserve_original// option. This option allows the filter to emit the unmodified token at the some position allowing more precise searches if the query includes diacritics.
NOTE: ICU folding can be enabled today only for the completion suggester (because //preserve_original// is not needed by the completion suggester)
(currently enabled on greek wikipedia)