To use the keyboard, install AutoHotKey (https://www.autohotkey.com/), and then double-click Yiddish.ahk to open it. You can switch between Yiddish and English keyboards using the capslock key. (Shift-capslock will activate caps lock as normal). 

The keyboard is based on Isaac Bleaman's Yiddish Klal layout, with some optimizations for typing efficiency and convenience. Namely, the input is closer to the YIVO transliteration standard (e.g. 'y' as an alternate input for yud, rather than pasekh tsvey yudn). A few other keys have been moved around as well, such as moving shin to shift+S rather than W, and putting bare alef (for starting words with yud and vov) on otherwise unused Q.

The layout is easy to edit to customize it how you like! If you open Yiddish.ahk in Notepad (by right clicking), you can add and change lines to change the layout. 

Each line takes the form:
:c*:(Latin letter)::(Hebrew Letter)
e.g.
:c*:m::מ

For shift shortcuts, simply use the capital letter:

:c*:M::ם

AutoHotKey offers powerful text replacement rules, which in future versions will allow for automatic text replacement, like adding shtumer alef at starts of words, or changing letters to final forms at the end of words. 

To turn off the keyboard, go to your system tray (the arrow on the right of the task bar), find the green box with an S, right click and terminate the script.