X_I18N_FAMILY_INCOMPLETE
Means
a select or ordinal family has no _other
Typical cause
a catalog defines <key>select<value> or <key>ordinal<category> keys and no <key>_select_other or <key>_ordinal_other, so a value the family does not name renders the loud miss
Fix
x i18n check --json — then add <key>_select_other (or <key>_ordinal_other) to the catalog it names