Right. But this is not Jowett's problem. Any translator has to apply his understanding to the text, that is to interpret or 're-create' it, if we may say so. Knowing the original, you understand a mixture of Plato and Don, while by the translation the mixture becomes Plato, Jowett and Don, with Plato in a greater distance, since Jowett stands in the middle.
As best I can make out, though, Plato sometimes uses different words for "temperance" and "wisdom", implying that these two virtues differ and have differing definitions. For example, we have Book IV of the Republic where, at 427e-34d, Plato claims that his city will be wise, brave, temperate, and just. Could we please do yet another fill-in-the-brackets exercise with the following quotes (this time, from Paul Shorey's translation)?
428e. "Then it is by virtue of its smallest class [the philosopher guardians] . . . and the wisdom () that resides therein, in the part which takes the lead and rules, that a city established on principles of nature would be wise () as a whole."
429b-c. Though apparently irrelevant to the question I'm raising, I note here Plato's claim that the city will be brave in that its guardians will protect the principles inculcated in them through education, rather than from motives of pleasure and pain.
430e. "Soberness () is a kind of beautiful order and a continence of certain pleasures and appetities, as they say, using the phrase 'master of himself' . . ."
433b. "This, then . . . appears to be justice, this principle of doing one's own business." (As I've noted earlier, Plato has Charmides and Critias suggest in the Charmides dialogue at 160b that temperance is doing one's own business.)
Evidently, all these virtues are conceptually linked, having to do in one way or another with restraint of passions and adherence to correct standards. Despite these linkages, though, Plato seems in this key Republic passage to construe wisdom and temperance as different.
428e. "Then it is by virtue of its smallest class... and the wisdom (episteme) that resides therein, in the part which takes the lead and rules, that a city established on principles of nature would be wise (sophe) as a whole."
430e. "Soberness (sophrosene) is a kind of beautiful order and a continence of certain pleasures and appetities, as they say, using the phrase 'master of himself'"
I was astounded by 428e, ". . . the wisdom (episteme) that resides therein . . ." On Shorey's English translation, we appareently had two senses of one word; and the implied link seemed to suggest a reason why the city would be ". . . wise (sophe) as a whole". In reality, though, we had two different words and no link and therefore no special reason.
It's always humiliating to see the results of these fill-in-the-brackets exercises, which generate results I had not expected. Working from translations, I've come to fancy myself as well-versed in things Platonic. But evidently this approach has blinded me to important points. I do wish I had learned Greek.