Want to localize an animation in a real location, want to know if it's possible to import height maps from i.e. Google or other suitable sources. 

Of course. You will even get Height scale, offset and smoothness options when you import height map...

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There is an internal tool in v6?
Searching for custom terrain maps I find only references to Earth Sculptor in iC v5.

Well, not exactly, but: http://manual.reallusion.com/iClone_6/ENU/Pro_6.0/default.html

(you have terrain templates already in iClone, and with changing height-map texture, you are actually terraforming.) 

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Thanks.
Reading "Replacing textures to change landscape" is good for height map but I can't change the materials distribution to adapt to the new map without Earth Sculptor.
I didn't find it in the RL store, the plugin is always available? Need I to purchase the full application?

Sorry to say, here my knowledge (better say memory) about EarthSculptor dies... Didnt touch it for years. What I do is to make somewhere else (in any modeler) terrain mesh, with all textures tuned in Photoshop, and then import in iClone as ordinary prop. Wrong, memory consumption considering everything but smart, but it worked when I needed. (but never needed so accurate terrain.)

Sorry. 
Hope someone with more terraforming experience will jump in...

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Earth Sculptor is the key - you can use the demo version.

Here is a Tutorial that explains how to do it:

https://www.youtube.com/channel/UCWeQl4nB8ul5RvXIs4HZ5Ig

Start with "Importing Google Maps" 
Then play "Roughing in Terrain Parts 1 & 2"

You can download the Earth Sculptor demo here:

http://www.earthsculptor.com/download.htm

Meaning I didn't want to create an animation in a phantasy created terrain, but in a real location, where I can use real maps to approximate terrain heights, vegetation and buildings location.

You don't need Earth Sculptor to change the materials distribution. Any paint program, such as Photoshop, that is capable of creating a .PNG file with transparency can do the job. The terrain mask works on a simple Red/Green/Blue concept. Red corresponds to Material 01, Green Corresponds to Material 02, Blue corresponds to Material 03 and black corresponds to Material 04. If you have a paint program that creates layers, you can have a layer for each color; that way you can turn a layer on/off to create effects such as snow in the winter.

Here is a terrain mask I created in Corel Photo-Paint.