Hey Héctor, I'll take a swing at this:

Retreat, Ongoing : In this game, when your armies keep retreating, the loss of terrotory will be ongong.

Rush, Depletion, Foe: We need to rush, There was a reduction of temperature, the foes are forming.

For this sentence, it would sound more natural to use the word "reduction" in stead of "depletion" as it relates to temperature. It works but I don't hear depletion used in that context as often. 

Among: Among other things, I'm grateful that you're reading this.

Thats pretty solid. 

Surmise: He surmised the answer to the enigma.
Decipher: I'm perfect at hiding things, for example, you can't decipher what I want to say in English.

Widely: I don't have a wide knowledge of your culture, so please be patient.

Widely could work in a sentence like: Your culture isn't as widely known so please be patient because I'm still learning about it. 

Brand: Do you prefer brand name clothes? Or do you not mind?

Hopefully this helps! Maybe someone else can come along and add their own insight.