E-Mail Notification language

How can i modify the notification language?

Problem:
User 1 set language german :Public e-mail notification is going out in german.
International recipient cannot read it because he can not speak German.

I want to set the default language to english. I found the code in the template editor, but i´m not a php coder.

> <table cellspacing="0" cellpadding="0" border="0" width="100%">
> <tr><td>
> <table cellspacing="0" cellpadding="0" border="0" width="600px">
> <tr>
> <td bgcolor="<?php p($theme->getMailHeaderColor());?>" width="20px">&nbsp;</td>
> <td bgcolor="<?php p($theme->getMailHeaderColor());?>">
> <img src="<?php p(\OC::$server->getURLGenerator()->getAbsoluteURL(image_path('', 'logo-mail.gif'))); ?>" alt="<?php p($theme->getName()); ?>"/>
> </td>
> </tr>
> <tr><td colspan="2">&nbsp;</td></tr>
> <tr>
> <td width="20px">&nbsp;</td>
> <td style="font-weight:normal; font-size:0.8em; line-height:1.2em; font-family:verdana,'arial',sans;">
> <?php
> **print_unescaped($l->t('Hey there,<br><br>just letting you know that %s shared <strong>%s</strong> with you.<br><a** href="%s">View it!</a><br><br>', [$_['user_displayname'], $_['filename'], $_['link']]));
> if ( isset($_['expiration']) ) {
> 	p($l->t("The share will expire on %s.", [$_['expiration']]));
> 	print_unescaped('<br><br>');
> }
> // TRANSLATORS term at the end of a mail
> p($l->t('Cheers!'));
> ?>
> </td>
> </tr>
> <tr><td colspan="2">&nbsp;</td></tr>
> <tr>
> <td width="20px">&nbsp;</td>
> <td style="font-weight:normal; font-size:0.8em; line-height:1.2em; font-family:verdana,'arial',sans;">--<br>
> <?php p($theme->getName()); ?> -
> <?php p($theme->getSlogan()); ?>
> <br><a href="<?php p($theme->getBaseUrl()); ?>"><?php p($theme->getBaseUrl());?></a>
> </td>
> </tr>
> <tr>
> <td colspan="2">&nbsp;</td>
> </tr>
> </table>
> </td></tr>
> </table>

I know that code snippet is responsible: ($l->t

How can i modify it that the notification is going out in english?