The Bilingual Keyboard Conflict
If you type in multiple languages on your Mac (for example, switching between an English QWERTY keyboard and a Spanish or Japanese input source), macOS attempts to streamline your workflow by associating specific input languages with specific applications or documents. If you have a document open in Pages where you previously typed in Spanish, and you switch from Safari (using English) back to Pages, macOS will often automatically change the input language back to Spanish. While this seems smart in theory, it frequently results in users typing a full sentence of gibberish because the OS silently swapped the keyboard layout beneath their fingers when they changed windows.
Enforcing a Global Input Source
To maintain consistent typing behavior and stop macOS from automatically changing your input language based on the active application, you must configure the Keyboard settings to treat the entire system uniformly.
Click the Apple logo in the top-left corner and select System Settings (or System Preferences). Scroll down the left sidebar and click on Keyboard. In the main panel, look under the “Text Input” section and click the Edit… button next to “Input Sources.” A new dialogue window will appear listing all your installed languages. Look at the bottom of this window for a setting labeled Automatically switch to a document’s input source. Uncheck this box. By disabling this, macOS will no longer attempt to remember which language you used in which app. The input language you select in the menu bar will apply globally to every single window and application on your Mac until you explicitly change it yourself.