Should I enter data as English and then translate to my language?
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.