Untranslatable String in Preferenceswindow.glade

[ghost]

Hi, I came across with this untranslated string in MyPaint. It is actually has been translated on Po files. But there is a mistake that don't apply the translation.

Basic system details

MyPaint version: 2.1.0-alpha+git.90b36db (via AppImage)
Operating system: Ubuntu 20.04
Desktop environment: GNOME

Steps to reproduce

1. Start MyPaint
2. Change language to Turkish (Or Esperanto, Portuguese, Spanish, Swedish. Because these are fully translated)
3. Open: Menu -> Duzenle -> Tercihleri Duzenle -> Dugmeler

You can see there one untranslated string.

The issue related with this lines:

mypaint/gui/preferenceswindow.glade

Lines 380 to 381 in b6c6eb7

	<property name="label" translatable="yes" context="Prefs Dialog|Button|Pointer Button Mappings|">• The space bar can be used like Button2.
	• Some tablet pads' buttons cannot be held down when pressed.</property>

I have tested on Turkish, Spanish, Portuguese langueges. This string always seems untranslated.

Screenshots: