"In the Greek language, we use a stress mark (tonos) on vowels to show which syllable is stressed. The normal search of Wikipedia returns articles that differ from the entered string only on stress, which is the expected behaviour. For example, if you enter ανεμος the first search result is άνεμος. However, the CompletionSuggester does not suggest άνεμος or any other word that starts with ά. It does, however, return ανεμοδαρμένος, ανεμούριο, ανεμοβλογιά, ανεμοστρόβιλος and several other words that start with an alpha without a stress mark. Rentzepopoulos (talk) 11:22, 8 March 2016 (UTC)"
I can confirm that the completion suggester beta feature is not taking these stress marks into consideration when presenting possible matches.
Potentially related task: T75605