Why is it wrong?
Across the board? In all cases?
Here are a few verses that come to mind.
Ephesians 4:29
Let no corrupting talk come out of your mouths, but only such as is good for building up, as fits the occasion, that it may give grace to those who hear.
Colossians 3:8
But now you must put them all away: anger, wrath, malice, slander, and obscene talk from your mouth.
James 5:12
But above all, my brothers, do not swear, either by heaven or by earth or by any other oath, but let your “yes” be yes and your “no” be no, so that you may not fall under condemnation.
Proverbs 13:3
Whoever guards his mouth preserves his life; he who opens wide his lips comes to ruin.
James 3:10
From the same mouth come blessing and cursing. My brothers, these things ought not to be so.
Exodus 20:7
“You shall not take the name of the Lord your God in vain, for the Lord will not hold him guiltless who takes his name in vain.
Matthew 5:33-37
“Again you have heard that it was said to those of old, ‘You shall not swear falsely, but shall perform to the Lord what you have sworn.’ But I say to you, Do not take an oath at all, either by heaven, for it is the throne of God, or by the earth, for it is his footstool, or by Jerusalem, for it is the city of the great King. And do not take an oath by your head, for you cannot make one hair white or black. Let what you say be simply ‘Yes’ or ‘No’; anything more than this comes from evil.
2 Timothy 2:16
But avoid irreverent babble, for it will lead people into more and more ungodliness,
Matthew 5:37
Let what you say be simply ‘Yes’ or ‘No’; anything more than this comes from evil.
Galatians 5:19-21
Now the works of the flesh are evident: sexual immorality, impurity, sensuality, idolatry, sorcery, enmity, strife, jealousy, fits of anger, rivalries, dissensions, divisions, envy, drunkenness, orgies, and things like these. I warn you, as I warned you before, that those who do such things will not inherit the kingdom of God.
Hebrews 4:12
For the word of God is living and active, sharper than any two-edged sword, piercing to the division of soul and of spirit, of joints and of marrow, and discerning the thoughts and intentions of the heart.
Acts 16:1-40
Paul came also to Derbe and to Lystra. A disciple was there, named Timothy, the son of a Jewish woman who was a believer, but his father was a Greek. He was well spoken of by the brothers at Lystra and Iconium. Paul wanted Timothy to accompany him, and he took him and circumcised him because of the Jews who were in those places, for they all knew that his father was a Greek. As they went on their way through the cities, they delivered to them for observance the decisions that had been reached by the apostles and elders who were in Jerusalem. So the churches were strengthened in the faith, and they increased in numbers daily. ...
1 Peter 3:10
For “Whoever desires to love life and see good days, let him keep his tongue from evil and his lips from speaking deceit;
Romans 12:14
Bless those who persecute you; bless and do not curse them.
James 3:9-10
With it we bless our Lord and Father, and with it we curse people who are made in the likeness of God. From the same mouth come blessing and cursing. My brothers, these things ought not to be so.
Psalm 10:7
His mouth is filled with cursing and deceit and oppression; under his tongue are mischief and iniquity.
James 1:26 ESV
If anyone thinks he is religious and does not bridle his tongue but deceives his heart, this person's religion is worthless.
In reality, one does not need verses. With the Holy Spirit as a guide, the answer should be clear and immediate.
Yes, in all cases it shows a lack of English skills to use curse words. Look at the spelling and quality of grammer in some posts we get.