One member of the CAS Panel actually was a native English speaker. But as someone who works abroad and deals every day with non-native speakers using English in a legal context, a few of whom handle international arbitration cases in English before tribunals in various different countries. I can tell you that there are many such people who have excellent English, in some cases better than many posters on here.
Putting the boot on the other foot, I've appeared as an expert witness in two Russian court cases. On each occasion, I'd first been questioned as a witness at length and produced a witness statement. I did that without an interpreter, but asked for an interpreter in the first court case - not because I needed it, but because I thought it would be handy if I needed to disrupt the flow of clever defence lawyers who were trying to discredit me. But in fact it didn't work out like that and I dispensed with the interpreter on the second occasion.
Both times, the court fully understood and was able to evaluate the evidence I gave, and the CAS arbitrators will have had no linguistic problem whatsoever in performing their functions. You've mentioned the language issue more than once and seem to think it has some relevance. I completely disagree.
The PL's Rules, by the way, may not specify a limitation period but nonetheless are subject to the Limitation Act 1980, which specifies a general limitation period of six years. However, under
section 32(1) of that Act, where an action is based on fraud or the deliberate concealment of relevant facts, the limitation period runs from the time when the fraud or concealment is discovered.
City will therefore argue that everything outside a six-year period is time-barred. The PL must be relying on concealment here and will no doubt maintain that the period should run from the time of the Der Spiegel leaks, when it first became aware of the matters at hand.
Meanwhile, I've just done a quick search and seen that you've referred seven times to Swiss law in the context of the CAS proceedings. I'm rather puzzled as to why you seem to think it matters at all. The fate of the PL's case ultimately comes down to the quality of the evidence that both parties will adduce.