Check bn (বাঙালি) 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 169_bn_locale
- Commit and create PR

Start with the Bengali locale file `_18n/bn.yml`, following the repository's Jekyll locale layout and the example `_18n/en.yml`. Review the Bengali text for typos and language errors, then verify that the file remains valid YAML; done means the corrections are committed on the requested branch and submitted as a pull request.

Written by the indexing model from the issue text.