The problem is, what happens if just one manual is translated incorrectly, which leads to an incident. I won't call it an accident, because if the crew followed the incorrectly translated instructions to the letter.......
Well in a lot of countries pilots study for their licences using the local language, from PPL up to and including ATPL, does that causes incidents?
Lots of manuals are written with English being the foreign language, does this causes incidents?