Since April 2017

We strongly recommend all users to use the Isis template. The Hathor template has not been updated to work with the new features shipping with this release.
When we released Hathor it was build with accessibility in mind, but over the years the Isis template has been improved in terms of accessibility and supporting technologies. We now believe that the Isis template is as good as or possibly better than Hathor.
To ensure a smooth experience for our users, during the update process, the default administrator template will be switched to Isis. You are free to switch this back after the update but we cannot guarantee and in fact know that many features will not work with Hathor.

This solution has the advantage of not modifying the lang strings.
But, normally, we should use a sprintf and modify the label string to include a br and a variable which would load the desc.
This Pr is not only for hathor...

or convert it to be a popover to be consistent with other fields.

hmm
at this time, using isis or Hathor, we do have correctly

Firefox Macintosh.

But, as @Quy says we can use popover to normalise with other tips

			<div class="control-label">
				<?php JHtml::_('bootstrap.popover');
					$text        = JText::_('COM_USERS_USER_FIELD_TWOFACTOR_LABEL');
					$description = JText::_('COM_USERS_USER_FIELD_TWOFACTOR_DESC');
					$position    = null;
					$title       = ' title="' . htmlspecialchars(trim($text, ':')) . '"'
						. ' data-content="'. htmlspecialchars($description) . '"';

					if (JFactory::getLanguage()->isRtl())
					{
						$position = ' data-placement="left" ';
					}
				?>
				<label id="jform_twofactor_method-lbl" for="jform_twofactor_method" class="hasPopover"
						<?php echo $title; ?><?php echo $position; ?>>
					<?php echo JText::_('COM_USERS_USER_FIELD_TWOFACTOR_LABEL'); ?>
				</label>
			</div>

@Kostelano
Are you going to update your PR with the code I provided or shall we close this and I will make a new PR?

Yes of course. I apologize for not being able to answer earlier.
I changed this according to your recommendation.
Everything works, thank you.

There are issues with wrong end of line and a concat code style