Translation:We are going to define the rules of the game.
No, that is not what the Spanish means, that form would be "¡Definamos las reglas del juego! http://conjugueur.reverso.net/conjugaison-espagnol-verbe-definir.html
"Vamos a + verb" is always "We are going to +verb" http://spanish.about.com/od/usingparticularverbs/a/ir_expressions.htm
That's not true. Vamos a ir can mean we are going to go or let's go, whereas no vamos a ir can only mean we are not going to go. "THE ULTIMATE SPANISH REVIEW AND PRACTICE, PREMIUM THIRD EDITION, McGRAW-HILL EDUCATION, 2016, P. 169" sorry this isn't a link but i pretty much quoted it directly.
I think "We're going to / We will" is different from "Let's." The "will / be going to" forms express what you believe is very probable to come about (insofar as future events can be predicted), and it may or may not include the addressee. As for "let's," on the other hand, it's more likely to be used as a suggestion, or an attempt to influence the addressee to make your desired plans become their shared plans. For example, if there are two speakers, and if #1 asks "What are you doing tomorrow?" and #2 answers "I don't know yet," it is OK for #1 to say "Let's..." in response (and it necessarily includes the addressee), whereas it's not OK for #1 to say "We will / We're going to" on the interpretation where "We" includes the addressee. (By the same principle, the Rolling Stones didn't sing "We're going to spend the night together"!) Does Spanish have a "Let's..." type of construction, for including the addressee and as an attempt to persuade them to do something with the speaker?
My issue is completely different than all others. Mine is about how to pronounce "juego". My table of sounds says the "j" is to sound like the english "h". My audio lesson from "Living Language" also uses the "h" sound. "SpanishD!ctionary.com also uses the "h" sound. I can't even describe what sound duolingo uses for the "j". It shows up best on the slow audio. Is this a mistake or just some obscure local thing.
Some of duolingo's pronunciation comes from Argentine Spanish, where the j is a rasp in the back of the throat, similar to the kh sound in German. Another Argentine sound is the ll or sometimes the y, like yo, llamar, or ayudar. Most Spanish speakers say these with a y sound similar to English, while others do a raspy shz sound. This should help with pronunciation.