At a certain time, I thought it was impossible to do, then one day I came across, the way to do it, here and there. Here is the solution :
suppose you want to add the connected user name dynamically
1. Create the label :
2. Now add the label on your page like this :
<apex:page>
<!-- Begin Default Content REMOVE THIS -->
<h1>
<apex:outputText value="{!$label.Hello}">
<apex:param value="{!$user.userName}" />
</apex:outputText>
</h1>
<!-- End Default Content REMOVE THIS -->
</apex:page>
There is some problem with this therefore, especially when the text in the custom label contains the '
(single quote) character . There is eventually, a way to bypass it, look at the example below :
Conformément à l'article 121 – II de la loi no. 2012-387 du 22 mars
2012, l'indemnité forfaitaire pour frais de recouvrement en cas
de<br/>
40 euros par le décret no.2012-115 du 02/10/2012. Tout matériel ou
logiciel reste la propriété de {0} jusqu'au paiement<br/>
Aucun escompte ne sera accordée pour paiement anticipé<br/>
'{1} au capital de {2}, No. Siren : {3}, TVA CEE : {4}
To bypass the ' (single quote)char , we use another '(single quote) in the right place, just that.