A text file that displays strange symbols may have been interpreted with the wrong character encoding. Saving it immediately can preserve the wrongly interpreted text instead of resolving the problem. Keep the received file unchanged while testing how it should be opened.

Ask the originating application or sender which encoding was used if that information is available. A file extension such as .txt does not specify the encoding, and a language name alone may not settle the choice.

Choose an opening option for this file

In TextEdit on Mac, choose File, Open and select the file without opening it yet. Click Show Options and choose a value from Plain Text Encoding. Apple documents a Customise Encodings List option if the required choice is not visible.

Open the file and compare several known words, names or symbols with a reliable reference. Include characters outside ordinary English letters if those are where the problem appears. A paragraph that looks mostly readable can still contain damaged punctuation or names.

If the result is wrong, close without saving and reopen the unchanged source using a justified alternative. Keep brief notes of the tested encodings instead of repeatedly guessing through settings and losing track of the results.

Separate successful reading from conversion

Once the text is correctly interpreted, decide whether any conversion is actually needed. The receiving system may require a particular encoding, so confirm that requirement before creating a new saved version.

Use a separate filename for a converted copy and reopen it in the destination application. Check the same representative words again. This verifies the saved result rather than only TextEdit’s current display.

Apple also provides a global default for opening plain-text files in TextEdit settings. Avoid changing that default to solve one unusual file unless most of your work requires it.

If no supported interpretation produces the expected text, preserve the source and request a fresh export. Encoding selection cannot recreate characters already lost or replaced before the file reached you.

References: Apple: TextEdit character encoding.