About three months ago we added an English version of our, previously Japanese only, site under the subfolder /en/ we've tried to follow the sometimes incomplete best practices laid out by Google by adding alternate tags to all pages that are currently translated. The top page for instance has the following meta tags for language.

<link rel="canonical" href="/">
<link rel="alternate" hreflang="ja" href="/">
<link rel="alternate" hreflang="en" href="/en/">

While the English main page under /en/ has

<link rel="canonical" href="/en/">
<link rel="alternate" hreflang="ja" href="/">
<link rel="alternate" hreflang="en" href="/en/">

Alternate languages are setup in the sitemap. (as per Google's recommendations)

It seems however that Google absolutely refuses to show the English top page in results when the user is using English at google.com if you search you'll, as of this post, get the Japanese description and a title that Google has apparently invented instead of the title and description in the meta-tags for the /en/ index page.

Does anyone have any experience with subfolders actually working to affect search results? What are the best practices for ensuring that the correct language version of my website is displayed through Google and other search engines? And how long will it take before the new language version becomes prominent in search engine results?