The SAGA plugins are still installed, but are nowhere to be found - until the Processing plugin is activated:
Now you have a new Processing menu, where you can turn on the Toolbox like this:
So now you have a full menu of geospatial algorithms, including those we've all studied in GIS courses using ESRI products; you can tweak the variogram model, block or cellsize (for different sampling resolutions).
One thing to note: these interpolations allow temporary files to be written, because we often "test and discard" our stat models. However if you don't remember to save your "good" interpolations as add them as a layer, when you quit - or, at least on my machine, QGIS crashes (all. the. time) - you lose your beautiful kriging. Attention.
That's it, perhaps en français later.