As chamanv said, pressing alt= LEFT_SHIFT switches between languages. This is a window that changes the keyboard layout. To go back just press alt= LEFT_SHIFT
More permanent solution:
To permanently disable this shortcut in Windows 10, go to Settings> Time and Language> Region and Language> Advanced Keyboard Settings> Language Panel Settings> Advanced Key Settings, and then click the Change key Sequence button Change key Sequence and set the value to " Not Assigned
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