Gabor Hojtsy, Drupal developer and employee #1 at Acquia, is the Drupal 8 Multilingual Initiative lead. A Drupalist since 2003, Gabor has assembled and sustained a large (1300 contributors!) global team that has made multilingual one of the most anticipated features in Drupal 8.
Most significant D8 contribution
For Drupal 8 I responded to Dries's call for leadership on multilingual improvements. What I enjoyed most about leading the Drupal 8 Multilingual Initiative was organizing the work and filling the gaps. And of course I also enjoyed spreading all the great things that the team of over 1300 people has accomplished.
Biggest challenge with D8
In my talk at DrupalCon Barcelona about how we organized the multilingual initiative, I highlighted the Views team. Initially I was very scared because it felt like Views might overshadow the rest of us. I even emailed people about it. It was bad. It was a true learning experience for me, and of course it turned out to be the total opposite of what I expected - so I sent an email about that too :). If not for Views, many of the great possibilities in Drupal 8's multilingual system would be nonexistent. The way we worked with each other and empowered each other turned out to be amazing.
Most looking forward to about D8
All the pieces coming together is really exciting: how more use of fields and fieldable things slide into using Views, which slide into using blocks for everything, which slides into deploying it all with configuration -- and all with multilingual support. I really love when the pieces come together like that. Drupal 8 will be a real pleasure for people to use to build things.