Add bangla translation

[AminulBD]

This is "Bangla" language translation.

Wiki:

1. https://en.wikipedia.org/wiki/International_Mother_Language_Day
2. https://en.wikipedia.org/wiki/Language_Movement_Day
3. https://en.wikipedia.org/wiki/Bengali_language_movement

[tareqas]

Hi @AminulBD thank you for your contribution. You know, translation can be subjective. So I proposed some changes that I believe will enhance the quality of our Bengali translation.

[AminulBD]

Hi @tareqas bunch of thanks to you. I did too much typing mistake and less expressive. thank you for your suggested changes.

[tareqas]

Thank you

[javiereguiluz]

@AminulBD thanks a lot for this contribution. We love adding new languages to the demo project. And, when they use non-Latin scripts, we like them even more because it helps us a lot to make sure that everything works as it should.

Tareq, thanks also to you for the great review and fixes/tweaks that you did in this contribution.

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