Other mistake: Angel implies that Wesley told him the device will kill Illyria. But this Angel is from earlier in the timeline, as shown when he tries to tell Wes and Spike things they have just told their Angel. So Wes did not tell this Angel that the Mutari generator will kill Illyria. Angel should know nothing about it.
Other mistake: The Chinese writing shown tattooed all over Wo-Pang's body is nonsense (a small number of random characters repeatedly jumbled together), although Wesley reads it as if it is language. (Although one might argue that the writing is meant to be some sort of code, there is no evidence in the show itself to suggest that, and Wesley refers to "translating" rather than "decoding" it; for these reasons it is more likely to be simply a mistake rather than an intentional decision.)