Hi, let me help you.
Are the documents actually opening with Chinese characters that look like real language, or is it garbled symbols and boxes that don't seem to be real text?
If it's real Chinese text appearing (like the file's language or the app's UI switched), that's often a regional/language setting issue — either the document itself has a language tag set to Chinese, or the application's display language got changed. If it's garbled symbols, that's a character encoding mismatch — the file was likely saved in one encoding (like UTF-8 or GB2312) and is being opened by an app that's guessing the wrong one.
It'd also help to know what kind of documents these are — Word files, PDFs, plain text, emails, something else — and whether this happens with files from one particular source or across different files.