Translation:He is going to play soccer with his brother.
French construction: jouer à + game "au" is the contraction of à-le.
- il joue au tennis
- il joue à la balle
sports & games: jouer à la balle (fem), jouer au football (masc sing, contraction of 'à+le'), jouer aux échecs (masc plur), jouer aux fléchettes (fem plur)
Non-native speakers beware. When an American talks about football they mean American Football. They say soccer to mean Associaton ("European") Football. Brits talk about football for the latter game. Glad to see Duo accepts both!
To be more precise, North American people say "soccer" to mean non-US football. South American football (soccer) teams are among the top best in the world and African football (soccer) is also of very high quality. So it is definitely not a European thing.
Soccer and football are the same thing in England but football wasn't accepted in my answer.
Why doesn't this translate into "He is playing soccer...", "He will" seems to be the future tense?
"he is playing soccer" is "il joue au football" or "il est en train de jouer au football" - present tense / continuous
"he will play soccer" is indeed a future tense, to be translated by "il jouera au football".
"il va jouer au football" can be understood 2 ways: either he is actually going (walking, riding...) to the stadium or he is "on the verge of" starting a game.
Also "he will play soccer with his brother" because "aller" is also used to talk about events that will happen in the future
"Aller + infinitive" is the near future and the English near future is "to be going to + verb".
-" He will play soccer"" is simple future and translate to the French simple future: "il jouera au football"