Apple - How can I set up a keyboard shortcut for switching input source?

Go to System Preferences → Keyboard → Shortcuts → Input Sources and define a keyboard shortcut there. As you only have two sources, set a single shortcut for one of the options, then pressing the shortcut will toggle the input sources.

grgarside's answer was great.

Here is an another solution for multilingual user. If you want to switch among three or more input methods quickly or switching to a specific input method by shortcut directly, you may try IMEShortcuts (disclaimer: I'm the IMEShortcuts creator)

It allows you map a shortcut to a input method. You can switch to a specific method immediately by you-defined shortcut without using cmd+space to rotate input methods. It works well on OSX 10.9 ~ 10.12.

Please have a try, I'm glad to hear your feedback. Thanks

If you are using Apple's Bangla keyboard, you can type English by holding down the Option/alt key. If you are using Bangla Qwerty, you can do this by pressing the Caps Lock key.