Firstly, am I correct to assume that Hose doesn't do any damage other than knockback and potentially inflict the Prone condition?
Correct.
Secondly, is exactly how do you use Language skill?
Language skills come in 4 ranks.
• "Basic" knowledge in the language
• "Specialist" in the language
• "Expert" at that language
• "Native" language" (you typically only have one at this level)
Language (understanding spoken or written things that you would not understand without knowledge in the language) is resolved with a perception test.
Are you suppose to roll it every time someone talks to you?
Basically, yes.
At the second level you gain a positive dice pool modifier of 2 dice to your perception test.
At the third level you gain a positive dice pool modifier of 3 dice to your perception test.
You don't take tests for your native language.
The thresholds of tests to understand languages is based on the Threshold Guidelines table, p. 36.
Elements such as the volume and speed people use when speaking or the amount of slang/lingo employed can affect the threshold.
does the Armor Spell stack with worn Armor Gear?
Yes.
Say, for example, if I have a Body 2 and armor that gives me DR 3, and then I cast Armor with 3 Hits would that give me a DR of 8?
Yes.