A pet peeve I have about bad translation is when a family member describes a patient's pain without asking the patient first. The worst example is when I asked the patient to point with one finger to where her pain was. Instead of asking his wife, the husband just reached out and pointed to a location on her back with one finger.
I don't think I know my husband well enough that I could pinpoint his pain with one finger. Then again, we haven't been married for 40 years like this couple probably was. So... yeah, that's something to look forward to.
In any case, this is why family members should not be the translator.