Our website supports 4 different languages.
I've enabled the human friendly settings in the web.config so the URL of our product page is converted to http://www.cantillana.com/products.aspx instead of http://www.cantillana.com/Products/tabid/57/language/nl-BE/Default.aspx.

But as you can see the language is gone in the URL. Is it possible to include this in the human friendly URL?

Would it be better to use child portals instead?
For instance, my parent portal is in English and my other languages are child portals (nl.cantillana.com, fr.cantillana.com, ...)

One thing to consider when using 2 parent portals to handle ML is that data is isolated by portal. That means that you will have 2 sets of users, 2 sitemaps, 2 site settings, etc. Impacts on SEO should also be considered as you will work with 2 differents domains, each evaluated separately for page rank.

Our open source localization extensions will enable you to implement ML inside a single portal, by creating a branch of pages for each language. It will produce SEO friendly URLs (in which the language is the first part of the URL, such as /en/Home.aspx). It will enable the use of the "copy page" function to copy the page for translation, which separate portals will not enable.

The free friendly Url provider or Url Master software from ifinity.com.au is a must. It will produce better URLs than the HumanFriendly feature of the DNN one.