Languages in/around Mythic Europe

I didnt knew about the translation requirements (A&A 87). So 6 in both languages and Area Lore 3(in the Book Language Area). Here is some info:

Better some examples to clarify your proposal.
2 persons both talk same dialect at effective level 5 communicate with a + 2 bonus.
2 persons both talk same "dialect", one level 4; the other level 3. They get a +2 bonus (same dialect) and a -3 penalty (under 5), so -1
2 persons both talk same language at effective level 5 communicate with a - 2 bonus.
2 persons both talk same "language", one level 4; the other level 3. They get a -2 bonus (different dialect) and a -3 penalty (under 5). so -5

I understand this bonus/penalty applies only must be aplied to the "Player" Die Roll, in order to succeed whatever purpose. Im not sure now, but seems It does not make sense to penalize both characters, as the total effect should add to 0. Perhaps in some cases this is fine, need to imagine different situations (NPC wants to cooperate with PC / NPC wants to win the point to the PC / and so on)

Seems a house rule (2x different language penalty) can be used as a base for the XP free gain, representing this double effect (lets say speaking / listening). For example, a 6 in Catalan, could default to 4 (50 XP free) in any other Occitan language, to 2 (15 XP free) in any "Western Romance" language, to None in others.