WIP: Add i18n

[astagi]

This PR adds i18n support. It's a work in progress, cause it needs some things to be completed:

• Some hard coded labels to translate
• Define a list of languages the app should support
• Understand how to get the correct view and edit urls based on language. The current interpolation under off.js doesn't work for some languages (e.g. https://world-en.openfoodfacts.org/cgi/product.pl?type=edit&code=26041254 gives an error)

[raphael0202]

Thanks for the PR 👍, I've added a few comments

[raphael0202]

Sorry I didn't see this was a WIP

[astagi]

No problem @raphael0202 I updated the PR with new translations and the requested changes

[astagi]

@raphael0202 I marked "Understand how to get the correct view and edit urls based on language." as done, looks like @teolemon is working to fix the problem in #57

[teolemon]

Erm I'm very unfamilar with Vue.JS. Feel free to fix the issue in this pr

[teolemon]

But the PR already LGTM to me

[astagi]

@teolemon that's good ✌🏻 Also if 'en' is the only case where view and edit links fail, you can write that part of code with a single line expression

`https://world${lang === 'en' ? '' : '-' + lang}.openfoodfacts.org/product/${barcode}`

[raphael0202]

Sorry for the delay. A few translations are missing in en.json for the logo search page, but I will add them manually. Merging, thank you!

[astagi]

Thanks @raphael0202 👍 sorry for missing translations, I didn't see them 👀 I'll check the missing item "Define a list of languages the app should support", supported languages can be added manually later