I said about someone that I thought someone was related to him but I said a bad name linked towards him that some people used not understanding (at that point) it was bad . It’s a name in another language. But straight afterwards I realised I was saying something bad . Is this counted as backbiting ?
If you say something that the other person will hate to hear then it is known as backbiting.
In your case, if you had spoken a bad word then it will be counted as backbiting even if it is in any other language.
You can just repent and Allah would forgive you. Allah is the forgiver of all sins.
May Allah Grant You Jannah. Asalamualaikum...
As you said you didn't understand the meaning of the word at that time then it is not your mistake. In Islam, if you do anything unintentionally then there is no sin for that.
Prophet Muhammad (SAWW) once said, "The reward of deeds depends upon the intention and every person will get the reward according to what he has intended."