When creating a new taskchain activity, Moodle complains about missing strings with the following error message :

Help title string does not exist: [nameadd, taskchain]
line 513 of /lib/outputcomponents.php: call to debugging()
line 1930 of /lib/outputrenderers.php: call to help_icon->diag_strings()
line 1695 of /lib/formslib.php: call to core_renderer->help_icon()
line 2169 of /home/moodle/plugins/mod/taskchain/edit/form/helper/base.php: call to MoodleQuickForm->addHelpButton()
line 687 of /home/moodle/plugins/mod/taskchain/edit/form/helper/record.php: call to taskchain_form_helper_base->add_helpbutton()
line 337 of /home/moodle/plugins/mod/taskchain/edit/form/helper/record.php: call to taskchain_form_helper_record->add_template_textsource()
line 1281 of /home/moodle/plugins/mod/taskchain/edit/form/helper/base.php: call to taskchain_form_helper_record->add_field_name()
line 1162 of /home/moodle/plugins/mod/taskchain/edit/form/helper/base.php: call to taskchain_form_helper_base->add_field()
line 1136 of /home/moodle/plugins/mod/taskchain/edit/form/helper/base.php: call to taskchain_form_helper_base->add_section()
line 57 of /home/moodle/plugins/mod/taskchain/mod_form.php: call to taskchain_form_helper_base->add_sections()
line 191 of /lib/formslib.php: call to mod_taskchain_mod_form->definition()
line 71 of /course/moodleform_mod.php: call to moodleform->moodleform()
line 261 of /course/modedit.php: call to moodleform_mod->moodleform_mod()
Invalid get_string() identifier: 'nameadd' or component 'taskchain'. Perhaps you are missing $string['nameadd'] = ''; in mod/taskchain/lang/en/taskchain.php?
line 6725 of /lib/moodlelib.php: call to debugging()
line 7421 of /lib/moodlelib.php: call to core_string_manager->get_string()
line 1951 of /lib/outputrenderers.php: call to get_string()
line 101 of /lib/outputrenderers.php: call to core_renderer->render_help_icon()
line 1936 of /lib/outputrenderers.php: call to renderer_base->render()
line 1695 of /lib/formslib.php: call to core_renderer->help_icon()
line 2169 of /home/moodle/plugins/mod/taskchain/edit/form/helper/base.php: call to MoodleQuickForm->addHelpButton()
line 687 of /home/moodle/plugins/mod/taskchain/edit/form/helper/record.php: call to taskchain_form_helper_base->add_helpbutton()
line 337 of /home/moodle/plugins/mod/taskchain/edit/form/helper/record.php: call to taskchain_form_helper_record->add_template_textsource()
line 1281 of /home/moodle/plugins/mod/taskchain/edit/form/helper/base.php: call to taskchain_form_helper_record->add_field_name()
line 1162 of /home/moodle/plugins/mod/taskchain/edit/form/helper/base.php: call to taskchain_form_helper_base->add_field()
line 1136 of /home/moodle/plugins/mod/taskchain/edit/form/helper/base.php: call to taskchain_form_helper_base->add_section()
line 57 of /home/moodle/plugins/mod/taskchain/mod_form.php: call to taskchain_form_helper_base->add_sections()
line 191 of /lib/formslib.php: call to mod_taskchain_mod_form->definition()
line 71 of /course/moodleform_mod.php: call to moodleform->moodleform()
line 261 of /course/modedit.php: call to moodleform_mod->moodleform_mod()
Help title string does not exist: [tasknamesadd, taskchain]
line 513 of /lib/outputcomponents.php: call to debugging()
line 1930 of /lib/outputrenderers.php: call to help_icon->diag_strings()
line 1695 of /lib/formslib.php: call to core_renderer->help_icon()
line 2169 of /home/moodle/plugins/mod/taskchain/edit/form/helper/base.php: call to MoodleQuickForm->addHelpButton()
line 687 of /home/moodle/plugins/mod/taskchain/edit/form/helper/record.php: call to taskchain_form_helper_base->add_helpbutton()
line 419 of /home/moodle/plugins/mod/taskchain/edit/form/helper/record.php: call to taskchain_form_helper_record->add_template_textsource()
line 1281 of /home/moodle/plugins/mod/taskchain/edit/form/helper/base.php: call to taskchain_form_helper_record->add_field_tasknames()
line 1162 of /home/moodle/plugins/mod/taskchain/edit/form/helper/base.php: call to taskchain_form_helper_base->add_field()
line 1136 of /home/moodle/plugins/mod/taskchain/edit/form/helper/base.php: call to taskchain_form_helper_base->add_section()
line 57 of /home/moodle/plugins/mod/taskchain/mod_form.php: call to taskchain_form_helper_base->add_sections()
line 191 of /lib/formslib.php: call to mod_taskchain_mod_form->definition()
line 71 of /course/moodleform_mod.php: call to moodleform->moodleform()
line 261 of /course/modedit.php: call to moodleform_mod->moodleform_mod()
Help contents string does not exist: [tasknamesadd_help, taskchain]
line 516 of /lib/outputcomponents.php: call to debugging()
line 1930 of /lib/outputrenderers.php: call to help_icon->diag_strings()
line 1695 of /lib/formslib.php: call to core_renderer->help_icon()
line 2169 of /home/moodle/plugins/mod/taskchain/edit/form/helper/base.php: call to MoodleQuickForm->addHelpButton()
line 687 of /home/moodle/plugins/mod/taskchain/edit/form/helper/record.php: call to taskchain_form_helper_base->add_helpbutton()
line 419 of /home/moodle/plugins/mod/taskchain/edit/form/helper/record.php: call to taskchain_form_helper_record->add_template_textsource()
line 1281 of /home/moodle/plugins/mod/taskchain/edit/form/helper/base.php: call to taskchain_form_helper_record->add_field_tasknames()
line 1162 of /home/moodle/plugins/mod/taskchain/edit/form/helper/base.php: call to taskchain_form_helper_base->add_field()
line 1136 of /home/moodle/plugins/mod/taskchain/edit/form/helper/base.php: call to taskchain_form_helper_base->add_section()
line 57 of /home/moodle/plugins/mod/taskchain/mod_form.php: call to taskchain_form_helper_base->add_sections()