Validating number with comma as decimal point 2

#### Support plan

* *is this issue currently blocking your project?* (yes/no):
* *is this issue affecting a production system?* (yes/no):

#### Context

* *node version*: 12.18.3
* *module version*: 17.2.1
* *environment* (e.g. node, browser, native):
* *used with* (e.g. hapi application, another framework, standalone, ...):
* *any other relevant information*:

#### What problem are you trying to solve?

I have exactly same problem like in issue #2017. How can I assign the the comma sign in 8701,5 as decimal point which is the default in Czechia?
Schema like bellow return "hodnota" must be a number. How to best approach this issue? Can separator mentioned in #2017 be implemented? Is some extension available?

```
const schema = Joi.object({
dn: Joi.number()
})
```

#### Do you have a new or modified API suggestion to solve the problem?