With such variation, finding text colors that stand out enough from the background is next to impossible. But you can't go wrong with plain white. Some people have to access the Web without graphics. Visually impaired readers can set the text size larger to make it easier to read. Blind people can use browsers that read the words to them or transliterate them into braille.
Search engines can index the words.
But pictures are meaningless to a reading machine or an indexing program. Some people have access only to Lynx or other text-only browsers, and others prefer to use a graphical browser with images turned off for speed and economy. When designing icons for navigation or other purposes, include text as part of the image. There's no point in avoiding language for your icons when the body of your pages must be in English or some other language. Some Web sites that have versions of their pages in several languages use flags as icons to indicate English, French, German, Spanish, and so on.