When browsing in LilyPondTool menu > Score > Use complete template, said templates are missing (nothing happens when selecting one).
I'm using the French-translated interface, could this be a localization problem?
No, I don't think it's localization. Does the same happen when choosing the template from the second step of the document wizard?
Nope, it works with the wizard.
The "complete" templates now depend strongly on the wizard values (like key signature), so that feature will be only accessible from the 2nd step on the wizard.