There are at least two problems with using translations of historical sources. The simplest is that sometimes the translator will clearly make a mistake. Thomas Johnes, the only man to translate all of Froissart since Lord Berners, did this a lot.
But even a good and scrupulous translator can be confronted with challenges that have no good solution. For example, a word in another language can have multiple meanings, each best translated by a different word in English. Sometimes the choice is clear from context, and sometimes it isn't, and the translator will need to make a decision. Any choice he makes will be false to the original.
Baston can mean club, rod, staff, baton or weapon in medieval French. If the passage is unclear about which the author meant, any one of the English choices will strip away the ambiguity of the original and quite possibly betray the intent of the original author.
So reading the source in the original language can be very valuable if you can do it.
More and more I've taken to noting the original word or phrase when I think my translation may be problematic.