Is there a term or an idiom for something similar to pointing at somebody else's weakness when that person has the same weakness?
An apt English idiom in this context is:
The pot calling the kettle "black."
The Dictionary.com entry tells us:
Criticizing others for the very fault one possesses: “I wouldn't call him lazy if I were you, Andy; that would be the pot calling the kettle black.”
Throwing stones in a glass house
Live in a glass house
One who is open to criticism should not criticize others, as in "It's stupid of Mike to mention his opponent's accepting donations from lobbyists — people who live in glass houses!" This proverb is so well known that it is often shortened.
Source: Dictionary.com (emphasis mine)
Criticizing other people for bad qualities in their character that you have yourself.
Source: Cambridge Dictionary
Criticizing other people for having the same faults that you yourself have.
Source: The Free Dictionary
Complaining about others if we are as bad as they are.
The generic term for that is hypocrisy.
- 1. a person who pretends to have virtues, moral or religious beliefs, principles, etc., that he or she does not actually possess, especially a person whose actions belie stated beliefs.
It actually has a couple of definitions but this is used to term the person considered in practice. If a person states weakness in others which he/she actually possess, then conversely he/she is giving a false impression of a strength that he/she does not possess.
The Mote and the Beam
The Mote and the Beam (also called discourse on judgmentalism) is a proverbial saying of Jesus given in the Sermon on the Mount. in the Gospel of Matthew, chapter 7, verses 1 to 5. The discourse is fairly brief, and begins by warning his followers of the dangers of judging others, stating that they too would be judged by the same standard.