You can always improve Text/HTML ratio by adding more content to your website. More than this percent is likely to be consider as spam.Show more An ALT attribute represents information about the image if it is not available or till its loading.
THEAD section of a table, the table header is a great resource for the Search Engine crawler to identify the content of the table.
Its great that you have a header for your table columns to identify them uniquely.
Search Engines detect the language in which your website has been written, which increases its regional importance as well helps it understand the text.
Therefore, it is a must to incorporate language tag and you must make sure you that Google detects your webpage language the same as specified by you.
Furthermore, it helps the developer by not having to dig through code to find CSS specification. Nowadays, most social plugins use IFrames, and its content is not indexed therefore it doesn't matter much.