Smannesman: Different religions may use different idioms, but they're not 'mere grammar'.
They're belief systems and a way of life, calling them anything else might not be in tone with the topics title.
Everything is a "belief system" and a "way of life", this is not relevant here. The point is that their content (let's say their moral content) fluctuate a lot, and can be dressed up with various different "belief systems". You can refer, for instance, to a belief in "hell" and "paradise", yet hold the same discourse content (in terms of moral obligations) as a person who doesn't. That level of representation ("belief system") is accessory, and can be switched for several others, while retaining the same message and the same prescriptions. Structurally, it's a simple change of flavor, of form, for what actually matters underneath. So yes, it does function like a language. And focusing too much on that form instead of the content is what generates useless oppositions and cross-accusations. As if "which word is used for that" was more important than the intended meaning.