Stephen,
In Unicode, there is not a one-to-one relationship between bytes in a file and characters (except that in UTF-8 encoding the standard 128 ASCII characters are directly mapped to the same bytes they are in 8-bit ASCII). This allows for more than 256 standardly defined code points. There are currently more than 100,000 defined, and the current specification allows for more 1,000,000. A capital Eth in the Icelandic language (Ã) is always code 00D0 (hexadecimal), and is stored as 00D0 in UTF-16 and C390 in UTF-8. The different encodings (UTF-8, UTF-16, and others) are just different ways of representing the same Unicode characters in data. If text is mostly Chinese with a small amount of English, UTF-16 encoding would be more compact, whereas text that is mostly English with a little bit of Chinese would take up less space stored as UTF-8.
Before Unicode and multibyte fonts, non-ASCII characters would be mapped often arbitrarily to different code points in a font, creating a sort of cipher text (like how the Wingdings font replaces "Y" with the Star of David, and Zapf Dingbats puts the same character in place of "A"). Fonts mapped in this way were often interdependent with the text that used them - the text made no sense unless rendered with that particular font.
With Unicode, there is no ambiguity about the intended character represented by a code, and the only concern between one font and the next (other than aesthetic considerations) is wether one or the other contains a glyph for all of the characters to be used. If the Unicode specification existed from the beginning of time, Wingdings and other "pi" fonts would probably be empty in the normal ASCII range, because there is a defined Unicode code for "smily face," "skull & cross-bones," and "ridiculous-looking ornamental detritus."
The data is probably stored by Excel natively as Unicode, and when the file is saved as UTF-16 text (not CSV - all non-ASCII characters would change to underscores), the raw text is preserved as English and Chinese in Unicode, without any font information at all.
The poster's file probably looks okay in one application because it is showing all of the text in a font that contains all necessary glyphs, or using a different font for just the Chinese characters because it knows the default font is missing glyphs for them.
In Indesign, it sounds like everything is in Futura, which lacks glyphs for the Chinese characters and probably shows them as squares. If the poster changes just these characters to another font, they can keep Futura for all of the English and display the Chinese in another font.
If you are using OS X, run Terminal.app from Applications/Utilities, then type "man grep" and return, and you can read the manual for the Unix program "grep," from which the Indesign find/replace option gets its name and copies its syntax. The manual is probably available online also.
rint:]]" (without the quotation marks), then click on the magnifying glass icon to the right of "Change Format:," and select the font for the Chinese characters.
