Das steht gleich zu Begin bei "help dblog".
#%dbconfig= (
# connection => "mysql:database=fhem;host=<database host>;port=3306",
# user => "fhemuser",
# password => "fhempassword",
# # optional enable(1) / disable(0) UTF-8 support
# # (full UTF-8 support exists from DBD::mysql version 4.032, but installing
# # 4.042 is highly suggested)
# utf8 => 1
#);
D.h. also den Schlüssel "utf8 => 1" setzen. Im Internal steht dann UTF8 auf "1".