No matter how devious the realms of herbal solutions and DEAR SIR notes, Digital Inspiration's filter is probably worth installing in your Gmail filters. Create a new filter by clicking Settings->Filter->Create a new filter in Gmail's web interface, then follow the linked post's instructions on pasting and setting up a system to archive and, optionally, apply a label to your non-English mail. For those of us who have no contacts who would write in another language, it's fairly safe to just delete or archive the filter-caught messages without a new label, but international mailers can use their discretion.
Looking at it again, the copy-friendly text included at the link below includes lang:en, which would filter out English language emails. Make sure you remove that snippets and the OR before or after it to ensure your standard English emails arrive in your inbox. In other countries and languages, be sure to remove the snippet relevant to your email language. Thanks, xxdesmus!
The bad news is that this filter will only catch emails that identify themselves in their headers, or embedded source information, as written in a language other than English. Spam mail has about the least reliable headers around, which is why thieves write messages from "PayPal Services" asking for your passwords. So don't expect to see everything cleaned away, but with a combination of this filter and Gmail's built-in spam management, you might ! get a cl eaner inbox. For more plug-and-play filter fun, try our ten must-have, download-ready Gmail filters.