In Brazil, the expression "to hide the gold" (Portuguese: "esconder o ouro") is used to express that someone is hiding his/her own talents or wealth, for modesty or because he/she doesn't want to be bothered because of those talents or wealth. Is the same expression used in English with the same meaning? If not, which's an equivalent expression?
You could say, they're trying to blend in with the crowd (go unnoticed).
Alternately, the expression keep a low profile might fit the bill.
keep a low profile: to stay out of public notice, avoid attracting attention to oneself. This expression alludes to profile in the sense of "a visible contour," a usage dating from the 1600s. [Late 1900s] The American Heritage® Dictionary of Idioms by Christine Ammer
It’s therefore interesting to note that those individuals who achieve fame and success on a long-term basis are those who have managed to live life with a great deal of humility and more importantly, to blend in with the crowd. They understand the abovementioned dangers and thus have often made efforts to steer clear of them by remaining humble. It’s quite an irony when you think about it because humble people usually keep a low profile when they communicate and thus they should have a lower chance of securing success for themselves, as compared to a more vocal individual who flaunt their strengths whenever opportunities arise Writing for Maximum Impact
In light of your comments below, consider using keep one's cards close to the vest/chest to fit your examples.
play one's cards close to one's chest and play one's cards close to one's vest; keep one's cards close to one's chest; keep one's cards close to one's vest
Fig. to keep to oneself or be very cautious in one's dealing with people. (As if one were playing cards and not permitting anyone to see any of the cards.) He is very cautious. He plays his cards close to his chest. You seem to be playing your cards close to your vest. McGraw-Hill Dictionary of American Idioms and Phrasal Verbs
From Matthew 5.15: to hide one’s lamp [or light] under a bushel. The expression is applied more to the modest concealment of extraordinary abilities than of wealth, though, and often with a hint of reproach.
This is attested (and glossed) as a common expression in British English at Cambridge, and in American English as well via Free Dictionary citing McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
"To hide gold" is not an idiomatic expression in the English language, though talent (originally a unit of weight for gold) has long been used to mean aptitude by reference to the parable of the talents, as discussed above. It may be that some of the sense of the Brazilian idiom could be captured by the phrase "still waters run deep" -- but the overlap is at most partial, and there may be no overlap at all.