I don't think everyone needs a fully translated/localised version of the OS but more and better support built into it. Such as keyboard mappings, localised alphabets, decimal sepertator handling (most non-English speaking languages use a , where English speakers use a . and vice versa).
I for one regularly switch between Icelandic, Swedish and Danish keyboard layouts on my Windows computer but doing so on RISC OS has been impossible for me - simply because current solutions are too difficult to optain and not feasible to use. I would like to see these localised settings built into the OS by default, not having to search the internet for possible solutions that some third party may or may not have written in the form of a module.
Support for different alphabets and correct decimal seperator in third party applications used to be appalling, pretty close to non-existant. Many software writers were quite willing to fix that once contacted but far too many simply were not interested, because they were not getting any sales outside UK/Australia/New Zealand, failing to realise that without correct handling of these issues the software was literally unusable in most countries. How things stand right now I don't know since my RiscPC is in a box over 2.000 Km away waiting to be used again (this summer it will be ).
Windows and Linux have an excellent, built in system for localisation that most software houses have realised exists and use quite well. If RISC OS is to stand a chance outside English speaking countries something similar must become available for the OS and software writers must use that support. Even only using whatever is already available would be an excellent start.