You can certainly enter Layout mode and specify a different font for layout text--such as field labels in your database, but this is probably a case where the actual characters typed in as field names are the cause of this problem. You can certainly rename the fields from inside Define Fields, but this could be a long, tedious process...
You may also want to try recovering your file in FileMaker 6 and then try converting the recovered copy to the .FP7 file that will be the first step of this conversion process.
A review of the conversion process:
First, you use FileMaker 11 to convert to .fp7 format, then you use Filemaker 12 to convert to .fmp12 format.
Here's a download link for a 30 day free trial copy of Filemaker 11 you can use for the first step of the conversion:
I also recommend that you read these two Knowledge Base articles on converting your files:
Converting to .fp7 format: http://help.filemaker.com/app/answers/detail/a_id/750/kw/converting
Converting to .fmp12 format: http://help.filemaker.com/app/answers/detail/a_id/10571/kw/converting
Be prepared to invest some time into testing and updating the converted files as there is a good chance that your converted files may not function perfectly. The KB articles cover many, but not all of the possible issues. Feel free to post back here with any issues you encounter that don't seem to have been covered by the KB articles.
Note: You should find a download link for a trial copy of the older FileMaker version that you can use to convert files inside the first of these articles.