I had a Fluency and Accents rules variant in 4e that saw a decent level of success for the intrigue game we were running.
"I approach the merchant and speak in Native Common with my Orc accent to increase my Intimidation check."
"That's a +4. Are you sprinkling in Orc words?"
"No Dwarven. You said he's a dwarf. Dwarven words since Orcish and Dwarven share scripts."
"That's another +2. Okay."
"Can you guys have a conversation in Working Elvish and slip in History or Culture advice as I intimidate?"
"You think a rich merchant doesn't have at least Professional Elvish?"
"I approach the merchant and speak in Native Common with my Orc accent to increase my Intimidation check."
"That's a +4. Are you sprinkling in Orc words?"
"No Dwarven. You said he's a dwarf. Dwarven words since Orcish and Dwarven share scripts."
"That's another +2. Okay."
"Can you guys have a conversation in Working Elvish and slip in History or Culture advice as I intimidate?"
"You think a rich merchant doesn't have at least Professional Elvish?"