This command line utility is for anyone needing the ability to change their system language programmatically. I originally wrote this while writing a program to facility learning another language.
The code is on github at ChangeInput.
A binary is included in the repo under build/releases. You can also download the project and build it yourself using Xcode. Xcode is free and can be downloaded from the App Store.
Example of using it from a Terminal prompt.
changeInput Spanish
=> Changed input language to Spanish
changeInput U.S.
=> Changed input language to U.S.