For e.g. if you want to change text lebel of "Academics" to "Academics Settings" in English language then go to the file path location \application\language\English\app_files and open system_lang.php file then serach for the keyword "Academics"
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Now replace it with "Academics Settings" then save it.
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After save changes it will look like below image at Smart School site.
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Note- Please make sure you have done changes in proper format (like Academics Settings must be under single inverted commas) otherwise code will cause an error.