Running s10u1_12 on Sparc:
Belgian keytable file "Belgian5.kt" is not present in keytables directory "/usr/openwin/etc/keytables/". According to sun docs: "http://docs.sun.com/app/docs/doc/817-2521/6mi67tj40?a=view" Belgian keyboard TYPE5 is supported. Also in keytable.map file Belgian5.kt entry is included.
When keyboard TYPE5 is switched for Belgian layout, missing keytable file causes that xserver can not be started.