When using the Solaris Live Upgrade luupgrade(1M) command with the -i option to complete an upgrade of an inactive boot environment, the text that the installers display might be unreadable in some languages. The text is corrupted when the installers request fonts that do not exist on the older release that is on the current boot environment.
Workaround: Choose one of the following workarounds:
Use a combined network installation image to do the installation.
Enable the C locale by setting the environment variable on your system.