Support multilingual pages via a toggle

On the website for [InterHop](https://interhop.org/en) made with Jekyll, there is an "EN/FR" button that allows switching between french and english language.

The code for that website is at [framagit](https://framagit.org/interhop/interhop-website). According to their README they're using [this](https://sylvaindurand.org/making-jekyll-multilingual/) to make the site mulilingual.

I was wondering if you would be interested in implementing this? If not, i'll do it for myself but would prefer to avoid diverging from your repo too much. Alternatively if you want me to make a PR just tell me.

Sort of related to #568