User Manual:Installing Extensions & Translations
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As of verison 3.2.2, extensions/add-ons/translations packaged as Qt Resource Files (.rcc) can be installed by dragging and dropping those files in the main window editor.
In prior versions, add-ons packaged as Qt Resource Files (.rcc) can be installed easily by opening the settings dialog, under Add-Ons tab, and clicking the "Import Add-On..." button. The add-on file (.rcc) is then installed. Restart KLatexFormula for the changes to take effect. New Languages may be selected in the "Appearance" tab before restart.