In bug report 226523 Greg V. proposed switching geany to gtk3 using an option. This was no possible due to not being able to force gtk3 in geany from the plugins.
I have built this patch set to leverage flavors, so that correct dependency chains can be enforced by pkg.
The devel/geany-plugins-l10n could actually be unflavored, but I am unable to find a way to make it unflavored and not break or pollute the dependency chain.