Corrected entry: Fon is deaf/mute in the film, as shown in many scenes she appears in. However in some scenes she responds to words Joe says. Especially in the scene where she tries to tell him her name.
Corrected entry: In the beginning scenes in Prague, just after Joe shoots the witness, there are several shots of witness's papers. One of them shows witness's head shot and the name spelled "JINDOICH EIPERA" (with a stroke-through O and accented E) which is wrong. This kind of erroneous spelling happens when Central European texts are printed with a Western/US character set. The correct spelling should be "JINDRICH CIPERA" (with R and C with caron).
Correction: So those papers were printed with a Western/US character set. Where's the movie mistake in that? We don't know who hired Joe to do the job in Prague, there's no reason the paperwork he was given could not have come from America.
I don't agree with the correction itself (a faulty transliteration is a mistake regardless), but this correction was probably made without seeing the scene. Those papers are not in Joe's possession, but the papers of the Prague police that arrested the witness he is killing before an interrogation. There's no reason for them to have papers that are written in the wrong character set.
Correction: She is looking at his face during those scenes. It's possible she's reading his lips.