The input methods are part of the main firmware - so if you want simplified chinese, try:
W850_R1KG001_MAIN_CHINA_CY_RED52 <- Main firmware
W850_R1KG001_FS_APAC_RED52 <- File system
HB1-06_Gen_CDA102568_101_R5A_GENERIC_APAC <- Cust pack
I don't have a W850 to check with, but if it's like any other DB2020 firmware, that should give you simplified Chinese both for input and menus.
You could also try the W850_R1KG001_FS_CMCC_RED52 filesystem - that will certainly have the files for Chinese support in it - but it will probably also have those ugly China Mobile menu icons and "let's make every button on the phone take you the Monternet wap portal" feature.