Minecraft translation files
In this example I will change the Return to game text of ESC menu.
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"menu.returnToGame": "Return to &aSurvival &fGamemode"
The languages property is used to list all the languages where you want to change the text. You should set it to only the languages of your playerbase, but I decided to set it to ALL so you will be sure that everyone can see the custom text despite their decided clientside language.