Android - Use bluetooth keyboard with a different layout?

You need to install physical keyboard layouts. One of the best extensions to do that is this:

RS - Hardware Keyboard Layouts

It is free, and does nothing else. You use the standard settings page to select the hardware keyboard layout.

(It is mystery why Google does not provide the layout files by default.)

The best way to use two different languages either on a smartphone or on a tablet is from device standard settings, with device keyboard and also with external USB and bluetooth keyboard. To use more than one language follow the images: [I can't post images yet]

General Settings -> Language and input -> Option of Samsung keyboard -> Input languages

Here you can chose between many languages. So you have setted correctly. Now to use one or the other language when you write is very easy, you have to slide with finger on the spacebar of the device keyboard.

You might wish to give the External Keyboard Helper a try. Take a look at this screenshot (click for large variant):

External Keyboard Helper External Keyboard Helper Layouts
External Keyboard Helper (source: Google Play; click images for larger variant)

That's just two of its setting screens. See the second entry in the first? Chose keyboard layout. That's what you are looking for. And it should only apply to the external keyboard, while leaving your "software keyboard" untouched.