Currently it support english and partial translations for german for stencils. You can see how the translation is done for the bpmn2 stencil set for example at
We are currently working on finilizing the Japanese translations and will only be able to claim that one as tested in Designer 2.2. There are more translation files which were done by community that we haven't tested out (would be nice if someone could verify / help with that).
To enable a specific locale settings right now in Designer you have to modify its web.xml, look for:
and change to ja_jp for Japanese and deploy the war again. Note however that these translation files do not include stencil set translations. We are working on that for Japanese for the next release.
Described change is working for me (Designer 2.2.), Japanese translation activated OK. I need another languages (sk_SK or cz_CZ), but I know the principle now. I'm not sure if we'll do this locationlization or we'll use default en_us. If localization will be done I'll let the community know. Thank you.