Usually, a perma-ban is preceded by a series of increasing duration bans for the same offence. If the player had been banned many times already in the past for using disallowed language, and was up to perma-ban for a next offence, then it unfortunately doesn't matter how minor the transgression was; if it was such that they'd receive even just a one day ban for it, but it was their umpteenth ban for the same action, then those are just the rules.
If they hadn't already had bans for language many times before this, then the offence in question would usually need to be very obvious, very harsh, and very unquestionably maliciously intended, to warrant a perma-ban off the bat.
I don't know the player or the situation but if the perma-ban genuinely seems to be a misappropriation of justice, then whoever their friends are need to get in touch with them and encourage them to make the phone call to Turbine about it. Their phone CS is generally very helpful and talking to someone for a review will ensure that the matter is handled with due fairness. That's really your best bet. Beyond that, you shouldn't be discussing disciplinary action on the forums, that in itself is against the CoC.
Rider, Fighter, Virgin, Lover; Watcher, Chaser, Bearer of Pain.
Victim tormented, Abused and Broken; Rise from the ashes and Hunt once again.
And Vengeance Be Thy Oath.