The gemara gives examples of cases where the eidim were not able to read the contract themselves, so we allow for others to read for them. It is not clear whether we are speaking of eidim who cannot read but fully understand the language, so that the reader only needs to read but does not need to translate, or can the eidim even have a translator. The Shach in C.M. 44:3 (at the end) explains that even the Rambam who seems to require the eidim to understand the language, doesn't mean to exclude the possibility of a translator. The Rambam is just saying that if the reader is reading a language that the witnesses don't understand without translating, it is not valid. But, just as we allow for a reader, we also allow for a translator. The Shach actually paskens that if we have no choice we will allow a gett to be read for the eidim and translated.
It seems to me that Tosafos 9b is meduyak like this Shach. Tosafos asks, how can we allow others to read for the eidim, it should qualify as eid m'pi eid. Tosafos should have answered that they are not testifying anything, they are merely reading. But instead Tosafos writes:
ולא הוי עד מפי עד שאין צריכין להעיד על עיקר המעשה אלא שאומר שכך כתוב בשטר
Tosafos seems to say that they are indeed testifying to something, but since they are not testifying about what happened, they are only testifying as to what is written in the shtar it is valid. This rationale should allow them not only to testify that what they are reading is accurate, but even that what they are translating is accurate. Hence, a raya to the Shach.