If you're asking about someone's nationality:
* Quelqu'un de nationalité bangladaise (someone of Bangladeshi nationality)
* Un Bangladais (a Bangladeshi person)
If you're referring to someone who is physically located in Bangladesh:
* Quelqu'un au Bangladesh (someone in Bangladesh)
If you're asking about someone's origin:
* Quelqu'un originaire du Bangladesh (someone originally from Bangladesh)
Remember to choose the translation that best fits the specific situation you're describing.