Hi Julien,
Regarding the max size of string, this is applicable only for key properties. i.e only the primary key you defined in the Odata service has this limitation in offline mode.
Since you are using SMP SP08 you could have a look at this documentation:http://help.sap.com/saphelp_smp308sdk/helpdata/en/88/9d29b3fac0456b812d86b5794c6e54/frameset.htm
Regarding the chinese characters are you saying that you can't send it using string? I haven't tried it my self sending different language. It would be good if you could raise a ticket to SAP on this issue.
Regards, Midhun
SAP Technology RIG
