AbdulAlhazred
Legend
That much is similar to rituals - the mechanics would have to be made more intense to act as a full on feat or skill power like benefit, in my opinion.
Ways to boost it might be other enhancement to aid other... allow it to be done as a minor, allow aid attack or aid defense without a roll. (this is actually in keeping with the paradigm spend the price get the effect)
What other benefits could one encapsulate in silent battlefield communication?
Well, there MIGHT now and then be a narrative concern with say being overheard while discussing tactics in combat. Your own 'battle speak' would tend to mitigate that. Its still pretty weak.
Frankly ALL linguistic elements of RPG scenarios fall into the same category. Any NPC could reasonably speak your language, the fact that they don't is merely a contrivance of the GM meant to produce some plot effect. You could learn 101 languages, the GM could still confront you with one you don't know if that's what he's determined to do. At best I think that learning languages falls into [MENTION=42582]pemerton[/MENTION]'s realm of "ways to signal your interests as a player", and that's not something that need be or should be regulated by scarce resources.