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Your suggestion touches on part of the subject and so does Nesrin's answer. This saying cannot be translated word for word. The idea is that people cannot tell who is really good and who is not, so we would be trespassing on Allah's territory when we make such a claim. To understand the phrase we can first look at commands in the Quran forbidding people from praising one another openly:

ألم تر إلى الذين يزكون أنفسهم، بل الله يزكي من يشاء ولا يظلمون فتيلا - النساء

فلا تزكوا أنفسكم، هو أعلم بمن اتقى - النجم


The other reason for not doing so is the possible corrupting effect on the object of praise, here is the full version of the Hadith that Nesrin quoted:

"‏أن ‏ ‏رجلا مدح صاحبا له عند النبي ‏ ‏صلى الله عليه وسلم ‏ ‏فقال ويلك قطعت عنقه إن كنت مادحا لا محالة فقل أحسبه كذا وكذا والله ‏ ‏حسيبه ‏ ‏ولا أزكي على الله تعالى أحدا "

Which effectively means that if you must praise someone you should say "I consider him to be such and such, and only Allah knows for sure"

In this light, the meaning of the phrase you requested is: "and we do not praise anyone's merits in sight of Allah's true knowledge". However, instead of translating the phrase, I suggest replacing it with another that conveys the spirit of the original one:

"Faithful scholars and righteous young people -and only Allah knows the real scholars and the truly righteous- .."

Notice that this example is slightly different from the title of my answer just to give a choice of different wordings.