Handle correctly i18n content on the blog

[Slashgear]

Currently we did not make the blog i18n ready.

• Each page lang is by default in fr even if some post are written in english. We should dynamically set the language based on the markdown property lang
• It is quite complex for reader to understand which article is in english
  • We could add the flag from uk in the title of every article ? 💡
  • We could show language of LFT with an emoji too
  • We should list which conference has been given in english in the conference page