The history buffer was defaulting to a normal GtkTextTagTable which was breaking stuff. This wasn't noticed before as a TalkatuTagTable is usually set up via glade.
# SOME DESCRIPTIVE TITLE.
# Copyright (C) YEAR THE PACKAGE'S COPYRIGHT HOLDER
# This file is distributed under the same license as the talkatu package.
# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
#
# Translators:
# Piotr Drąg <piotrdrag@gmail.com>, 2019
#
#, fuzzy
msgid""
msgstr""
"Project-Id-Version: talkatu\n"
"Report-Msgid-Bugs-To: \n"
"POT-Creation-Date: 2019-07-19 13:19-0500\n"
"PO-Revision-Date: 2019-07-19 18:19+0000\n"
"Last-Translator: Piotr Drąg <piotrdrag@gmail.com>, 2019\n"