asian character handling (utf16?)

WD cron: PDOException: SQLSTATE[HY000]: General error: 1366 Incorrect string value: '\xF4\x80\x80\x80 \xF4...' for [error]
column 'body' at row 1: UPDATE {apachesolr_index_entities_file} SET hash=:db_update_placeholder_0,
body=:db_update_placeholder_1
WHERE (entity_id = :db_condition_placeholder_0) ; Array
(
[:db_update_placeholder_0] => d2c39033902aabdcb21d590b93365893849ffa10a2f2c998eaddfa3b8885fc5d
[:db_update_placeholder_1] => 丝 绸 之 路

(and a lot more asian characters)

[:db_condition_placeholder_0] => 8644
)
in apachesolr_attachments_get_attachment_text() (line 103 of
sites/all/modules/apachesolr_attachments/apachesolr_attachments.index.inc).

I could find the responsible files, but the content is confidential, cannot share it here. I'll try to find a sample to reproduce this error securely.