Oh god...you're SERIOUSLY trying to say that any foul language is a red card?
You of all people? Really???
Please support your claim with a reference from FIFA/IFAB. Anything at all.
As for your comment above - I work in a customer service role in a business. There are things I can't say to customers - I certainly couldn't swear to them. Even though in my industry most of my customers probably swear more than me. But I can swear when talking to colleagues or my boss - although while tolerance shifts, there are still things I wouldn't be able to say to them.
Context. Players not in a customer service role minding out p's and q's.
The simple fact that IFAB made a deliberate language to remove the wording 'foul langauge' as a red card should itself be sufficient to tell you that IFAB no longer want foul language to be an automatic red card.
Although I have absolute certainty that you don't even buy what you're selling here and you're just being argumentative for the sake of it. After all, if you sent off every single player who said sh*t or f**k in any context on the field you'd have a lot of very, very short games.
I think the expectation is for the referee to consider what's roughly acceptable in the environment moreso than his own preferences. For instance, a particularly religious referee may be offended by player for saying 'Jesus!' on the field. And while technically permissible in the Laws, I would argue that the intent of the law isn't for him to ignore general accepted behaviour and force his own views.
But beyond that extreme example, yes, there is massive leeway. Context and volume matter. Level/age of match and the local environment as well.