Problem mit der Eingabe von Sonderzeichen (PDOException: SQLSTATE[HY000]: General error: 1366 Incorrect string value)

Hallo zusammen,

ich habe in Drupal 7 ein Problem mit der Eingabe von Sonderzeichen. Für die Übersetzung von Inhalten in eine slawische Sprache benötige ich diakritische Zeichen, z.B. ĕ, ć, ń oder ř. Bei der Eingabe dieser Zeichen in das Textfeld eines Inhaltstypen erhalte ich nach dem Abspeichern folgende Fehlermeldung:

PDOException: SQLSTATE[HY000]: General error: 1366 Incorrect string value: '\xC4\x95, \xC4\x87...' for column 'body_value' at row 1: INSERT INTO {field_data_body} (entity_type, entity_id, revision_id, bundle, delta, language, body_value, body_summary, body_format) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5, :db_insert_placeholder_6, :db_insert_placeholder_7, :db_insert_placeholder_8); Array ( [:db_insert_placeholder_0] => node [:db_insert_placeholder_1] => 243 [:db_insert_placeholder_2] => 244 [:db_insert_placeholder_3] => page [:db_insert_placeholder_4] => 0 [:db_insert_placeholder_5] => de [:db_insert_placeholder_6] => ĕ ć ń ř [:db_insert_placeholder_7] => [:db_insert_placeholder_8] => filtered_html ) in field_sql_storage_field_storage_write() (Zeile 425 von .../modules/field/modules/field_sql_storage/field_sql_storage.module).

Bei der Eingabe in das Titelfeld erhalte ich diese Fehlermeldung:

PDOException: SQLSTATE[HY000]: General error: 1366 Incorrect string value: '\xC5\x99' for column 'title' at row 1: UPDATE {node} SET vid=:db_update_placeholder_0, type=:db_update_placeholder_1, language=:db_update_placeholder_2, title=:db_update_placeholder_3, uid=:db_update_placeholder_4, status=:db_update_placeholder_5, created=:db_update_placeholder_6, changed=:db_update_placeholder_7, comment=:db_update_placeholder_8, promote=:db_update_placeholder_9, sticky=:db_update_placeholder_10, tnid=:db_update_placeholder_11, translate=:db_update_placeholder_12 WHERE (nid = :db_condition_placeholder_0) ; Array ( [:db_update_placeholder_0] => 244 [:db_update_placeholder_1] => page [:db_update_placeholder_2] => de [:db_update_placeholder_3] => ř [:db_update_placeholder_4] => 1 [:db_update_placeholder_5] => 1 [:db_update_placeholder_6] => 1300015239 [:db_update_placeholder_7] => 1300017883 [:db_update_placeholder_8] => 1 [:db_update_placeholder_9] => 0 [:db_update_placeholder_10] => 0 [:db_update_placeholder_11] => 0 [:db_update_placeholder_12] => 0 [:db_condition_placeholder_0] => 243 ) in drupal_write_record() (Zeile 6776 von .../includes/common.inc).

Der Datenbank für die Drupal-Installation ist der Zeichensatz utf8_general_ci zugewiesen. Der Response-Header der Seite zeigt ebenfalls den Zeichensatz utf8 an.
Hat jemand Ideen, wie sich das Problem beheben lässt. Für jedwede Anregungen und Hilfe wäre ich sehr dankbar.