Wrong font in GIMP user interface

[Joseph Maillardet]

On an updated Ubuntu Disco, Gimp does not use the font configured in Gnome-Tweaks.
I chose "Ubuntu Condensed Regular" font for the "Interface text".
Gimp displays a completely different font with serifs (See attached screenshot).
I also tested the "flathub" version of Gimp (flatpak install flathub org.gimp.GIMP). It has the same problem.
Gtk2 support broken ?

ProblemType: Bug
DistroRelease: Ubuntu 19.04
Package: gimp 2.10.8-2
ProcVersionSignature: Ubuntu 5.0.0-7.8-generic 5.0.0
Uname: Linux 5.0.0-7-generic x86_64
ApportVersion: 2.20.10-0ubuntu23
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Thu Mar 28 10:03:04 2019
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
SourcePackage: gimp
UpgradeStatus: Upgraded to disco on 2018-11-14 (133 days ago)

[Joseph Maillardet (jokx)]

Obviously, this is a problem with Gtk2 applications (see WinFF screenshot)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.