I didn't use it in practice, only for troubleshooting, but, what I'd do if I were on your place,
I would install the server with all the languages available, and tell the end users to use the language options in the browser to display the interface in their native language. Eclipse is not an issue, you can install the language extensions at any point if necessary.

Having said that, I cannot agree more with Ralph's remark about the added complexity with using multiple language clients. One thing that you should absolutely do, in my opinion, is to at least have the server generate logs in English. That will enable you to search through knowledge bases a lot easier, should an error occur.

The log language is determined by the -nl java parameter, as well as the server OS locale, depending on which log and which message are we talking about.