Looks like comp suggest is having some sort of json encoding problem? Perhaps php is structuring something in an unexpected way. These are not limited to a particular language, i see them for ja.wikipedia.org and de.wikipedia.org. These aren't all directly reproducable though, i tried pulling the url's from logstash and running them and they go through fine. Some sort of intermittent error.
Search backend error during comp_suggest search for '削除された 悪ふざけ' after 3: parsing_exception: Unknown key for a START_ARRAY in [suggest].