You have to put after ?ui=form the ?locale=fr, whith the ? before the parameter.
This is not explained in the bonita documentation, I think this is not serious. You have three kinds of URLS in the documentation in v6.X and any of them works for 6.3.0.
You can connect to Bonita BPM Portal from other tools using a URL of the form http://host:port/bonita#?..... Other forms of URL are liable to change in future versions. For example, use http://localhost:8081/bonita#?process=myProcessId&locale=fr, and do not use http://localhost:8081/bonita/console/homepage#?process=myProcessId&locale=fr
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