Often you have to have an understanding of the language to know how well it’s translated. It’s a bit circular.
But when you read such a tremendous translation effort it does indeed raise those thoughts.
it really depends on your goals. if you are just reading for pleasure, it can be lovely to just read a good translation as written. if you are approaching the text more seriously, you need to be aware that the translation of many key words can be quite controversial in these texts. to make matters worse, there are instances where the only copies of the text have been damaged and scholars have inferred letters or entire words. these reconstructions can also be controversial.
you don't necessarily have to become a fluent reader to get the most out of a particular text, but I would at least recommend reading the translation side-by-side with the greek, preferably with a good commentary to consult. sometimes the arguments in the commentary can be as interesting as the text itself!
[0] http://www.perseus.tufts.edu/hopper/text?doc=Xen.%20Anab.