Imants,
Sun does plan to add other locales to the Java Desktop System, however Latvian probably will not be in the next round of internationalizations. Perhaps this can come sooner if we work out a more streamlined process for sharing and validating internationalization efforts with the community. Thank you for your question!
Our translation team is still working on a good way to manage this. Until then, you might want to consider sharing your expertise with the gnome community. It looks like Latvian could use some help:
http://developer.gnome.org/projects/gtp/status/gnome-2.6/lv/
Thank you (or should I say Liels paldies?),
Brian