Steps to replicate the issue:
Open any non-English post on the Diff blog, e.g. 1.

What happens?:
The information in entry-meta (below title) remains in English, including the date and the word by to indicate authors.

What should have happened instead?:
The meta data should be translated according to the language of the post (selected through the language selector at the top of the page).

There are many other parts of the blog that lack internationalisation, as far as I can see. All parts should be translated eventually, but the meta data are the most important, as they are always displayed net to the translated title.