We have a tick box in Options->Configure->Unicode Input that says "Activate selected keyboard". I have come up with this from our interpreter code for that:
'loadkeyb'⎕NA'user32.dll|LoadKeyboardLayoutW <0T I4' ⍝ Then, for my locale of UK, I can use this to load our Unicode IME into the Dyalog process: loadkeyb'e0990809' 259 ⍝ For other keyboard layouts: loadkeyb'e0990406' 259 ⍝ DK loadkeyb'e0990407' 259 ⍝ DE loadkeyb'e0990409' 259 ⍝ US loadkeyb'e099040A' 259 ⍝ ES loadkeyb'e099040b' 259 ⍝ FI loadkeyb'e099040C' 259 ⍝ FR loadkeyb'e0990410' 259 ⍝ IT loadkeyb'e099041D' 259 ⍝ SE ⍝ To switch back to the standard English-United Kingdom layout: loadkeyb'00000809' 259