Should I enter data as English and then translate to my language? For data entry for taxonomy terms and field names should I enter data in English and then translate to my own language?Entering directly in my own language has no problem.I just want to know if there is any rule for this.
Well, if you've a only one language website, you can directly enter the values directly in your own language. You can also install your language pack that you can find on localize.drupal.org.

If you gonna start a multi-language website, you should (and its easier) to start everything in english and after start to translate. But in that case, is already important since the beginning to active all languages that you need.