i got the item for 10 wins per week in arena and this showed up in chat.

I don't do PvP so I'm not familiar with this part of the game.
Could you please explain in detail how this works? What item? Did you get a bonus roll window?

Alright, thanks for the info. I'm going to add these events to the ignore list as it's practically impossible to maintain a list for this.

I see, i found this: PVP_WEEKLY_BONUS_DESCRIPTION, which is used in Blizzard_PVPUI.lua.
This string is filled up with information of the function GetWeeklyPVPRewardInfo(bracketIndex)
local completed, itemLevel, numWins, numWinsReq = GetWeeklyPVPRewardInfo(self.bracketIndex)

Maybe its possible to get the possible rewards using
C_PvP.GetArenaRewards(teamSize) or
C_PvP.GetRatedBGRewards()
But i am note sure what this functions are exactly returning
The API documentations says this:
function C_PvP.GetArenaRewards(teamSize)
Part of the PvpInfo system
Arguments
1. number teamSize
Returns
1. number honor
2. number experience
3. (optional) table of BattlefieldReward rewards

structure BattlefieldReward
Part of the PvpInfo system
Fields
number id
string name
number texture
number quantity

So i could imagine that its possible to combine the returned itemlevel using GetWeeklyPVPRewardInfo(bracketIndex) with the rewards returned from C_PvP.GetArenaRewards,
but i am not sure, since the function C_PvP.GetArenaRewards doesn't return rewards while being in garrison 2.0 and i am not sure at which exact time/event this function is returning the rewards.

You get a random item which's itemlevel is based on the highest rating you achieved the week before. I did get a bonus roll window.
You get the item when the match is over and the scoreboard shows up.

Until I (or someone else) can figure out how to get loot data these events are ignored with a857f4a

See #41.