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.
Why do you look at the speck that is in your brother’s eye, but do not notice the log that is in your own eye?
Although this would indicate that the one who points out somebody else's weakness, not only has the same weakness, but has it with an even greater magnitude.
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.