how to customise error duplicate msg

Hello everyOne ;
i want to know how can i customise the error duplicate msg

Failure on the database. Please refer to sugarcrm.log file for details.

Thank u for ur help

Look for it in the language files.

for example if i want to integrate BOOTSTRAP to customise error page , how can i do ??

You could add custom css to display on the id/class for the error message.

What is the PATH of langage file ?
And where can i add the custom css ?
Can u give me more explanations plz