The glossary view with AJAX enabled in combination with Language detection by URL does not work. It appears the argument does not get applied.
For instance, clicking 'F' should filter nodes that start with F, however it loads all results as if no contextual filter was provided. If I disable URL detection -- thus making the POST http://example.com/views/ajax instead of http://example.com/en/views/ajax -- it works.
If I disable AJAX, the view works as it should (/glossary/f loads with F results). Other AJAX calls in the site with the language prefix do not cause any issue.