Why can I not restrict the available questions to a single language? I do not read Korean, Chinese, Japanese, Russian, etc. Only English.?

You are on the English language site, which has been gatecrashed by CHINESE spam posters. Only Yahoo/Verizon are in position to remove them - if they know how....

Because it's an English language site so no filters exist to help you avoid seeing questions that aren't supposed to be here.

The posts you refer to come from spam bots, but one or more humans are programming them. They are being paid by the company they are posting for, to enhance search engine optimization for that company (or so it appeared when the posts began a month or so ago). We don't know when or if Yahoo will take action. All we can do is report them, ignore them, or leave YA. The posts are ALL OVER the site. Hopefully they will be dealt with soon. MANY questions have been asked about this already (it amazes me so few people think to check in the Answers category to see if a problem with the site has already been addressed). The site's been heavily flooded with them since the weekend of July 7th.

By Default its set to English and Its against the Rules for people to Post in other Languages But Spammer Bots have been Breaking the Rules and Posting in Other Languages to Bother and Annoy other people Yahoo does not have any Filters for Languages set up Because of that

Because they are spam bots, posted here, it’s not a language glitch, it’s on purpose.

probably cause yahoo answers is all over the world, that might be why, i dont understand those languages either

There is no language selector on Yahoo. It can't be done.