This depends whether you are adventurous enough. If you understand the error, it means your PHP has some old class constructors.
OLD Php Class Constructor
Class myclassname {
    function myclassname() {
      //This is a constructor
    }
New Php Class Constructor 
Class myclassname {
    function __construct() {
      //this is the new constructor using __construct instead of the same function name as class name.
}
So what I did was to go into /usr/share/php/php-gettext/stream.php and /usr/share/php/php-gettext/gettext.php (or whatever file stated in your error), go to the file and change function myclassname() to function __construct.
The function myclassname should be identical to the CLASS myclassname declaration.
You should see about 4 errors if you are on ubuntu 16.04 with latest gettext. I just change that and it's not harmful to your system. It's a outdated programming syntax and if you upgrade in the future you wouldn't face any problem too. I will say it's a safe edit.
It's not really a major change or anything, just syntax updating. If you install from apt-get package you really have no other choice unless you compile yourself.
sudo nano /usr/share/php/php-gettext/streams.php
Line 48 StringReader Error.
Go to Line 52 and change 
function StringReader ($str='') {
TO
function __construct($str='') {
Line 84 FileReader Error
Go to Line 90 and change
function FileReader($filename) {
to 
function __construct($filename) {
Line 145 CacheFileReader error
Go to Line 146 and change
function CachedFileReader($filename) {
to
function __construct($filename) {
Using sudo nano /usr/share/php/php-gettext/gettext.php.
Line 36 gettext_reader { error
I think you get the gist now, go to line 101 and change
function gettext_reader($Reader, $enable_cache = true) {
To
function __construct($Reader, $enable_cache = true) {