There is a strange bug in Civ2 regarding costumized leader titles. As you noticed, it doesn't work properly if you change it in the rules.ger as stated in the comment above @LEADERS.
However, if you exchange the Plural name ("Romans") and the Adjective in the rules.ger [not in the scenario itself!], so the Romans' Adjective is "Romans" and the Plural name is "Roman", the leader titles should be recognized.
I didn't discover it myself, it was Gothmog whose newly moved
Civ2 site conveyed me this tip along others (see "Getting leader titles right")
P.S: There is also the possibility of changing this via hex editing, but its too complicated
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SCDARS
scenario_feedback@hotmail.com