What does it mean to learn a foreign language?

The significance of learning a foreign language:

This word is an obscure statement about whoring in the TV series "Citizen's Name", which is equivalent to a joint code. People can naturally understand it immediately, and people who eat melons often don't know the details, which plays a safer and more reliable role.

Source:

This word comes from the 23rd episode of in the name of people, when the vice chairman was arrested and Hegao sent the drunken Secretary-General Qin Ben away to find a foreign girl to learn a foreign language. Gao knew it was a foreign language, so he left. Subsequently, captain Qian of Guangming District Branch received a report from the masses and learned that he had been whoring again. He ordered that the matter must be strictly investigated.