Check bg (Български) locale and fix typos

Check locales by native and fix typos.

Project use [jekyll-multiple-languages-plugin](https://github.com/kurtsson/jekyll-multiple-languages-plugin). Each locale file are keeped in `_18n` folder.
For example `en` is located in `_18n/en.yml` file.

Project was translated by translation service not by human. So it can keep typos.

Need to check current issue language.

- Fork
- Create branch 168_bg_locale
- Commit and create PR

Start with the Bulgarian locale file under _18n, following the issue's example of _18n/en.yml. Review the current Bulgarian text for typos and commit the corrections on the requested branch, then create a pull request; done means the locale has been checked and corrected.

Written by the indexing model from the issue text.